Network Working Group C. Alaettinoglu
Request for Comments: 2280 USC/Information Sciences Institute
Category: Standards Track T. Bates
Cisco Systems
E. Gerich
At Home Network
D. Karrenberg
RIPE
D. Meyer
University of Oregon
M. Terpstra
Bay Networks
C. Villamizar
ANS
January 1998
Routing Policy Specification Language (RPSL)
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Table of Contents
1 IntrodUCtion 2
2 RPSL Names, Reserved Words, and Representation 3
3 Contact Information 6
3.1 mntner Class . . . . . . . . . . . . . . . . . . . . . . . 6
3.2 person Class . . . . . . . . . . . . . . . . . . . . . . . 8
3.3 role Class . . . . . . . . . . . . . . . . . . . . . . . . 9
4 route Class 10
5 Set Classes 12
5.1 route-set Class . . . . . . . . . . . . . . . . . . . . . . 12
5.2 as-set Class . . . . . . . . . . . . . . . . . . . . . . . 14
5.3 Predefined Set Objects . . . . . . . . . . . . . . . . . . 15
5.4 Hierarchical Set Names . . . . . . . . . . . . . . . . . . 15
6 aut-num Class 16
6.1 import Attribute: Import Policy Specification . . . . . . 16
6.1.1 Peering Specification . . . . . . . . . . . . . . . . . 17
6.1.2 Action Specification . . . . . . . . . . . . . . . . . 19
6.1.3 Filter Specification . . . . . . . . . . . . . . . . . 20
6.1.4 Example Policy EXPressions . . . . . . . . . . . . . . 24
6.2 export Attribute: Export Policy Specification . . . . . . 24
6.3 Other Routing Protocols, Multi-Protocol Routing
Protocols, and Injecting Routes Between Protocols . . . . . 25
6.4 Ambiguity Resolution . . . . . . . . . . . . . . . . . . . 26
6.5 default Attribute: Default Policy Specification . . . . . 28
6.6 Structured Policy Specification . . . . . . . . . . . . . . 29
7 dictionary Class 33
7.1 Initial RPSL Dictionary and Example Policy Actions
and Filters . . . . . . . . . . . . . . . . . . . . . . . . . 36
8 Advanced route Class 41
8.1 Specifying Aggregate Routes . . . . . . . . . . . . . . . . 41
8.1.1 Interaction with policies in aut-num class . . . . . . 45
8.1.2 Ambiguity resolution with overlapping aggregates . . . 46
8.2 Specifying Static Routes . . . . . . . . . . . . . . . . . 47
9 inet-rtr Class 48
10 Security Considerations 49
11 Acknowledgements 50
A Routing Registry Sites 51
B Authors' Addresses 52
C Full Copyright Statement 53
1 Introduction
This memo is the reference document for the Routing Policy
Specification Language (RPSL). RPSL allows a network operator to be
able to specify routing policies at various levels in the Internet
hierarchy; for example at the Autonomous System (AS) level. At the
same time, policies can be specified with sufficient detail in RPSL
so that low level router configurations can be generated from them.
RPSL is extensible; new routing protocols and new protocol features
can be introduced at any time.
RPSL is a replacement for the current Internet policy specification
language known as RIPE-181 [4] or RFC-1786 [5]. RIPE-81 [6] was the
first language deployed in the Internet for specifying routing
policies. It was later replaced by RIPE-181 [4]. Through
operational use of RIPE-181 it has become apparent that certain
policies cannot be specified and a need for an enhanced and more
generalized language is needed. RPSL addresses RIPE-181's
limitations.
RPSL was designed so that a view of the global routing policy can be
contained in a single cooperatively maintained distributed database
to improve the integrity of Internet's routing. RPSL is not designed
to be a router configuration language. RPSL is designed so that
router configurations can be generated from the description of the
policy for one autonomous system (aut-num class) combined with the
description of a router (inet-rtr class), mainly providing router ID,
autonomous system number of the router, interfaces and peers of the
router, and combined with a global database mappings from AS sets to
ASes (as-set class), and from origin ASes and route sets to route
prefixes (route and route-set classes). The accurate population of
the RPSL database can help contribute toward such goals as router
configurations that protect against accidental (or malicious)
distribution of inaccurate routing information, verification of
Internet's routing, and aggregation boundaries beyond a single AS.
RPSL is object oriented; that is, objects contain pieces of policy
and administrative information. These objects are registered in the
Internet Routing Registry (IRR) by the authorized organizations. The
registration process is beyond the scope of this document. Please
refer to [1, 15, 2] for more details on the IRR.
In the following sections, we present the classes that are used to
define various policy and administrative objects. The "mntner" class
defines entities authorized to add, delete and modify a set of
objects. The "person" and "role" classes describes technical and
administrative contact personnel. Autonomous systems (ASes) are
specified using the "aut-num" class. Routes are specified using the
"route" class. Sets of ASes and routes can be defined using the
"as-set" and "route-set" classes. The "dictionary" class provides
the extensibility to the language. The "inet-rtr" class is used to
specify routers. Many of these classes were originally defined in
earlier documents [4, 11, 14, 10, 3] and have all been enhanced.
This document is self-contained. However, the reader is encouraged
to read RIPE-181 [5] and the associated documents [11, 14, 10, 3] as
they provide significant background as to the motivation and
underlying principles behind RIPE-181 and consequently, RPSL. For a
tutorial on RPSL, the reader should read the RPSL applications
document [2].
2 RPSL Names, Reserved Words, and Representation
Each class has a set of attributes which store a piece of information
about the objects of the class. Attributes can be mandatory or
optional: A mandatory attribute has to be defined for all objects of
the class; optional attributes can be skipped. Attributes can also
be single or multiple valued. Each object is uniquely identified by
a set of attributes, referred to as the class "key".
The value of an attribute has a type. The following types are most
widely used. Note that RPSL is case insensitive and only the
characters from the ASCII character set can be used.
<object-name>Many objects in RPSL have a name. An <object-name>
is made up of letters, digits, the character underscore "_", and
the character hyphen "-"; the first character of a name must be a
letter, and the last character of a name must be a letter or a
digit. The following words are reserved by RPSL, and they can
not be used as names:
any as-any rs-any peeras
and or not
atomic from to at action accept announce except refine
networks into inbound outbound
Names starting with certain prefixes are reserved for certain
object types. Names starting with "as-" are reserved for as set
names. Names starting with "rs-" are reserved for route set
names.
<as-number>An AS number x is represented as the string "ASx". That
is, the AS 226 is represented as AS226.
<ipv4-address>An IPv4 address is represented as a sequence of four
integers in the range from 0 to 255 separated by the character
dot ".". For example, 128.9.128.5 represents a valid IPv4
address. In the rest of this document, we may refer to IPv4
addresses as IP addresses.
<address-prefix>An address prefix is represented as an IPv4
address followed by the character slash "/" followed by an
integer in the range from 0 to 32. The following are valid
address prefixes: 128.9.128.5/32, 128.9.0.0/16, 0.0.0.0/0; and
the following address prefixes are invalid: 0/0, 128.9/16 since 0
or 128.9 are not strings containing four integers.
<address-prefix-range>An address prefix range is an address
prefix followed by one of the following range operators:
^- is the exclusive more specifics operator; it stands
for the more specifics of the address prefix excluding the
address prefix itself. For example, 128.9.0.0/16^- contains
all the more specifics of 128.9.0.0/16 excluding
128.9.0.0/16.
^+ is the inclusive more specifics operator; it stands
for the more specifics of the address prefix including the
address prefix itself. For example, 5.0.0.0/8^+ contains all
the more specifics of 5.0.0.0/8 including 5.0.0.0/8.
^n where n is an integer, stands for all the length n specifics
of the address prefix. For example, 30.0.0.0/8^16 contains
all the more specifics of 30.0.0.0/8 which are of length 16
such as 30.9.0.0/16.
^n-m where n and m are integers, stands for all the length n to
length m specifics of the address prefix. For example,
30.0.0.0/8^24-32 contains all the more specifics of
30.0.0.0/8 which are of length 24 to 32 such as 30.9.9.96/28.
Range operators can also be applied to address prefix sets. In
this case, they distribute over the members of the set. For
example, for a route-set (defined later) rs-foo, rs-foo^+
contains all the inclusive more specifics of all the prefixes in
rs-foo.
<date>A date is represented as an eight digit integer of the
form YYYYMMDD where YYYY represents the year, MM represents the
month of the year (01 through 12), and DD represents the day of
the month (01 through 31). For example, June 24, 1996 is
represented as 19960624.
<email-address>is as described in RFC-822[8].
<dns-name>is as described in RFC-1034[16].
<nic-handle>is a uniquely assigned identifier[13] used by routing,
address allocation, and other registries to unambiguously refer
to contact information. person and role classes map NIC handles
to actual person names, and contact information.
<free-form>is a sequence of ASCII characters.
<X-name>is a name of an object of type X. That is <mntner-name>
is a name of a mntner object.
<registry-name>is a name of an IRR registry. The routing
registries are listed in Appendix A.
A value of an attribute may also be a list of one of these types. A
list is represented by separating the list members by commas ",".
For example, "AS1, AS2, AS3, AS4" is a list of AS numbers. Note that
being list valued and being multiple valued are orthogonal. A
multiple valued attribute has more than one value, each of which may
or may not be a list. On the other hand a single valued attribute
may have a list value.
An RPSL object is textually represented as a list of attribute-value
pairs. Each attribute-value pair is written on a separate line. The
attribute name starts at column 0, followed by character ":" and
followed by the value of the attribute. The object's representation
ends when a blank line is encountered. An attribute's value can be
split over multiple lines, by starting the continuation lines with a
white-space (" " or tab) character. The order of attribute-value
pairs is significant.
An object's description may contain comments. A comment can be
anywhere in an object's definition, it starts at the first "#"
character on a line and ends at the first end-of-line character.
White space characters can be used to improve readability.
3 Contact Information
The mntner, person and role classes, admin-c, tech-c, mnt-by,
changed, and source attributes of all classes describe contact
information. The mntner class also specifies what entities can
create, delete and update other objects. These classes do not
specify routing policies and each registry may have different or
additional requirements on them. Here we present the common
denominator for completeness which is the RIPE database
implementation[15]. Please consult your routing registry for the
latest specification of these classes and attributes.
3.1 mntner Class
The mntner class defines entities that can create, delete and update
RPSL objects. A provider, before he/she can create RPSL objects,
first needs to create a mntner object. The attributes of the mntner
class are shown in Figure 1. The mntner class was first described in
[11].
The mntner attribute is mandatory and is the class key attribute.
Its value is an RPSL name. The auth attribute specifies the scheme
that will be used
Attribute Value Type
mntner <object-name> mandatory, single-valued, class key
descr <free-form> mandatory, single-valued
auth see description in text mandatory, multi-valued
upd-to <email-address> mandatory, multi-valued
mnt-nfy <email-address> optional, multi-valued
tech-c <nic-handle> mandatory, multi-valued
admin-c <nic-handle> mandatory, multi-valued
remarks <free-form> optional, multi-valued
notify <email-address> optional, multi-valued
mnt-by list of <mntner-name> mandatory, multi-valued
changed <email-address> <date> mandatory, multi-valued
source <registry-name> mandatory, single-valued
to identify and authenticate update requests from this maintainer.
It has the following syntax:
auth: <scheme-id> <auth-info>
E.g.
auth: NONE
auth: CRYPT-PW dhjsdfhruewf
auth: MAIL-FROM .*@ripe\.net
The <scheme-id>'s currently defined are: NONE, MAIL-FROM, PGP and
CRYPT-PW. The <auth-info> is additional information required by a
particular scheme: in the case of MAIL-FROM, it is a regular
expression matching valid email addresses; in the case of CRYPT-PW,
it is a password in UNIX crypt format; and in the case of PGP, it is
a PGP public key. If multiple auth attributes are specified, an
update request satisfying any one of them is authenticated to be from
the maintainer.
The upd-to attribute is an email address. On an unauthorized update
attempt of an object maintained by this maintainer, an email message
will be sent to this address. The mnt-nfy attribute is an email
address. A notification message will be forwarded to this email
address whenever an object maintained by this maintainer is added,
changed or deleted.
The descr attribute is a short, free-form textual description of the
object. The tech-c attribute is a technical contact NIC handle.
This is someone to be contacted for technical problems such as
misconfiguration. The admin-c attribute is an administrative contact
NIC handle. The remarks attribute is a free text explanation or
clarification. The notify attribute is an email address to which
notifications of changes to this object should be sent. The mnt-by
attribute is a list of mntner object names. The authorization for
changes to this object is governed by any of the maintainer objects
referenced. The changed attribute documents who last changed this
object, and when this change was made. Its syntax has the following
form:
changed: <email-address> <YYYYMMDD>
E.g.
changed: johndoe@terabit-labs.nn 19900401
The <email-address> identifies the person who made the last change.
<YYYYMMDD> is the date of the change. The source attribute specifies
the registry where the object is registered. Figure 2 shows an
example mntner object. In the example, UNIX crypt format password
authentication is used.
mntner: RIPE-NCC-MNT
descr: RIPE-NCC Maintainer
admin-c: DK58
tech-c: OPS4-RIPE
upd-to: ops@ripe.net
mnt-nfy: ops-fyi@ripe.net
auth: CRYPT-PW lz1A7/JnfkTtI
mnt-by: RIPE-NCC-MNT
changed: ripe-dbm@ripe.net 19970820
source: RIPE
Figure 2: An example mntner object.
The descr, tech-c, admin-c, remarks, notify, mnt-by, changed and
source attributes are attributes of all RPSL classes. Their syntax,
semantics, and mandatory, optional, multi-valued, or single-valued
status are the same for for all RPSL classes. We do not further
discuss them in other sections.
3.2 person Class
A person class is used to describe information about people. Even
though it does not describe routing policy, we still describe it here
briefly since many policy objects make reference to person objects.
The person class was first described in [14].
The attributes of the person class are shown in Figure 3. The person
attribute is the full name of the person. The phone and the fax-no
attributes have the following syntax:
Attribute Value Type
person <free-form> mandatory, single-valued
nic-hdl <nic-handle> mandatory, single-valued, class key
address <free-form> mandatory, multi-valued
phone see description in text mandatory, multi-valued
fax-no same as phone optional, multi-valued
e-mail <email-address> mandatory, multi-valued
Figure 3: person Class Attributes
phone: +<country-code> <city> <subscriber> [ext. <extension>]
E.g.:
phone: +31 20 12334676
phone: +44 123 987654 ext. 4711
Figure 4 shows an example person object.
person: Daniel Karrenberg
address: RIPE Network Coordination Centre (NCC)
address: Singel 258
address: NL-1016 AB Amsterdam
address: Netherlands
phone: +31 20 535 4444
fax-no: +31 20 535 4445
e-mail: Daniel.Karrenberg@ripe.net
nic-hdl: DK58
changed: Daniel.Karrenberg@ripe.net 19970616
source: RIPE
Figure 4: An example person object.
3.3 role Class
The role class is similar to the person object. However, instead of
describing a human being, it describes a role performed by one or
more human beings. Examples include help desks, network monitoring
centers, system administrators, etc. Role object is particularly
useful since often a person performing a role may change, however the
role itself remains.
The attributes of the role class are shown in Figure 5. The nic-hdl
attributes of the person and role classes share the same name space.
The
Attribute Value Type
role <free-form> mandatory, single-valued
nic-hdl <nic-handle> mandatory, single-valued, class key
trouble <free-form> optional, multi-valued
address <free-form> mandatory, multi-valued
phone see description in text mandatory, multi-valued
fax-no same as phone optional, multi-valued
e-mail <email-address> mandatory, multi-valued
Figure 5: role Class Attributes
NIC handle of a role object cannot be used in an admin-c field. The
trouble attribute of role object may contain additional contact
information to be used when a problem arises in any object that
references this role object. Figure 6 shows an example role object.
role: RIPE NCC Operations
address: Singel 258
address: 1016 AB Amsterdam
address: The Netherlands
phone: +31 20 535 4444
fax-no: +31 20 545 4445
e-mail: ops@ripe.net
admin-c: CO19-RIPE
tech-c: RW488-RIPE
tech-c: JLSD1-RIPE
nic-hdl: OPS4-RIPE
notify: ops@ripe.net
changed: roderik@ripe.net 19970926
source: RIPE
Figure 6: An example role object.
4 route Class
Each interAS route (also referred to as an interdomain route)
originated by an AS is specified using a route object. The
attributes of the route class are shown in Figure 7. The route
attribute is the address prefix of the route and the origin attribute
is the AS number of the AS that originates the route into the interAS
routing system. The route and origin attribute pair is the class
key.
Figure 8 shows examples of four route objects (we do not include
contact.
Attribute Value Type
route <address-prefix> mandatory, single-valued,
class key
origin <as-number> mandatory, single-valued,
class key
withdrawn <date> optional, single-valued
member-of list of <route-set-names> optional, single-valued
see Section 5
inject see Section 8 optional, multi-valued
components see Section 8 optional, single-valued
aggr-bndry see Section 8 optional, single-valued
aggr-mtd see Section 8 optional, single-valued
export-comps see Section 8 optional, single-valued
holes see Section 8 optional, single-valued
Figure 7: route Class Attributes
attributes such as admin-c, tech-c for brevity). Note that the last
two route objects have the same address prefix, namely 128.8.0.0/16.
However, they are different route objects since they are originated
by different ASes (i.e. they have different keys).
route: 128.9.0.0/16
origin: AS226
route: 128.99.0.0/16
origin: AS226
route: 128.8.0.0/16
origin: AS1
route: 128.8.0.0/16
origin: AS2
withdrawn: 19960624
Figure 8: Route Objects
The withdrawn attribute, if present, signifies that the originator AS
no longer originates this address prefix in the Internet. Its value
is a date indicating the date of withdrawal. In Figure 8, the last
route object is withdrawn (i.e. no longer originated by AS2) on June
24, 1996.
5 Set Classes
To specify policies, it is often useful to define sets of objects.
For this purpose we define two classes: route-set and as-set. These
classes define a named set. The members of these sets can be
specified by either explicitly listing them in the set object's
definition, or implicitly by having route and aut-num objects refer
to the set names, or a combination of both methods.
5.1 route-set Class
The attributes of the route-set class are shown in Figure 9. The
route-set attribute defines the name of the set. It is an RPSL name
that starts with "rs-". The members attribute lists the members of
the set. The members attribute is a list of address prefixes or
other route-set names. Note that, the route-set class is a set of
route prefixes, not of RPSL route objects.
Attribute Value Type
route-set <object-name> mandatory, single-valued,
class key
members list of <address-prefixes> or optional, single-valued
<route-set-names>
mbrs-by-ref list of <mntner-names> optional, single-valued
Figure 9: route-set Class Attributes
Figure 10 presents some example route-set objects. The set rs-foo
contains two address prefixes, namely 128.9.0.0/16 and 128.9.0.0/16.
The set rs-bar contains the members of the set rs-foo and the address
prefix 128.7.0.0/16. The set rs-empty contains no members.
route-set: rs-foo
members: 128.9.0.0/16, 128.9.0.0/24
route-set: rs-bar
members: 128.7.0.0/16, rs-foo
route-set: rs-empty
Figure 10: route-set Objects
An address prefix or a route-set name in a members attribute can be
optionally followed by a range operator. For example, the following
set
route-set: rs-bar
members: 5.0.0.0/8^+, 30.0.0.0/8^24-32, rs-foo^+
contains all the more specifics of 5.0.0.0/8 including 5.0.0.0/8, all
the more specifics of 30.0.0.0/8 which are of length 24 to 32 such as
30.9.9.96/28, and all the more specifics of address prefixes in route
set rs-foo.
The mbrs-by-ref attribute is a list of maintainer names or the
keyword ANY. If this attribute is used, the route set also includes
address prefixes whose route objects are registered by one of these
maintainers and whose member-of attribute refers to the name of this
route set. If the value of a mbrs-by-ref attribute is ANY, any route
object referring to the route set name is a member. If the mbrs-by-
ref attribute is missing, only the address prefixes listed in the
members attribute are members of the set.
route-set: rs-foo
mbrs-by-ref: MNTR-ME, MNTR-YOU
route-set: rs-bar
members: 128.7.0.0/16
mbrs-by-ref: MNTR-YOU
route: 128.9.0.0/16
origin: AS1
member-of: rs-foo
mnt-by: MNTR-ME
route: 128.8.0.0/16
origin: AS2
member-of: rs-foo, rs-bar
mnt-by: MNTR-YOU
Figure 11: route-set objects.
Figure 11 presents example route-set objects that use the mbrs-by-ref
attribute. The set rs-foo contains two address prefixes, namely
128.8.0.0/16 and 128.9.0.0/16 since the route objects for
128.8.0.0/16 and 128.9.0.0/16 refer to the set name rs-foo in their
member-of attribute. The set rs-bar contains the address prefixes
128.7.0.0/16 and 128.8.0.0/16. The route 128.7.0.0/16 is explicitly
listed in the members attribute of rs-bar, and the route object for
128.8.0.0/16 refer to the set name rs-bar in its member-of attribute.
Note that, if an address prefix is listed in a members attribute of a
route set, it is a member of that route set. The route object
corresponding to this address prefix does not need to contain a
member-of attribute referring to this set name. The member-of
attribute of the route class is an additional mechanism for
specifying the members indirectly.
5.2 as-set Class
The attributes of the as-set class are shown in Figure 12. The as-
set attribute defines the name of the set. It is an RPSL name that
starts with "as-". The members attribute lists the members of the
set. The members attribute is a list of AS numbers, or other as-set
names.
Attribute Value Type
as-set <object-name> mandatory, single-valued,
class key
members list of <as-numbers> or optional, single-valued
<as-set-names>
mbrs-by-ref list of <mntner-names> optional, single-valued
Figure 12: as-set Class Attributes
Figure 13 presents two as-set objects. The set as-foo contains two
ASes, namely AS1 and AS2. The set as-bar contains the members of the
set as-foo and AS3, that is it contains AS1, AS2, AS3.
as-set: as-foo as-set: as-bar
members: AS1, AS2 members: AS3, as-foo
Figure 13: as-set objects.
The mbrs-by-ref attribute is a list of maintainer names or the
keyword ANY. If this attribute is used, the AS set also includes
ASes whose aut-num objects are registered by one of these maintainers
and whose member-of attribute refers to the name of this AS set. If
the value of a mbrs-by-ref attribute is ANY, any AS object referring
to the AS set is a member of the set. If the mbrs-by-ref attribute
is missing, only the ASes listed in the members attribute are members
of the set.
Figure 14 presents an example as-set object that uses the mbrs-by-ref
attribute. The set as-foo contains AS1, AS2 and AS3. AS4 is not a
member of the set as-foo even though the aut-num object references
as-foo. This is because MNTR-OTHER is not listed in the as-foo's
mbrs-by-ref attribute.
as-set: as-foo
members: AS1, AS2
mbrs-by-ref: MNTR-ME
aut-num: AS3 aut-num: AS4
member-of: as-foo member-of: as-foo
mnt-by: MNTR-ME mnt-by: MNTR-OTHER
Figure 14: as-set objects.
5.3 Predefined Set Objects
In a context that expects a route set (e.g. members attribute of the
route-set class), an AS number ASx defines the set of routes that are
originated by ASx; and an as-set AS-X defines the set of routes that
are originated by the ASes in AS-X. A route p is said to be
originated by ASx if there is a route object for p with ASx as the
value of the origin attribute. For example, in Figure 15, the route
set rs-special contains 128.9.0.0/16, routes of AS1 and AS2, and
routes of the ASes in AS set AS-FOO.
route-set: rs-special
members: 128.9.0.0/16, AS1, AS2, AS-FOO
Figure 15: Use of AS numbers and AS sets in route sets.
The set rs-any contains all routes registered in IRR. The set as-any
contains all ASes registered in IRR.
5.4 Hierarchical Set Names
Set names can be hierarchical. A hierarchical set name is a sequence
of set names and AS numbers separated by colons ":". For example,
the following names are valid: AS1:AS-CUSTOMERS, AS1:RS-EXCEPTIONS,
AS1:RS-EXPORT:AS2, RS-EXCEPTIONS:RS-BOGUS. All components of an
hierarchical set name which are not AS numbers should start with
"as-" or "rs-" for as sets and route sets respectively.
A set object with name X1:...:Xn-1:Xn can only be created by the
maintainer of the object with name X1:...:Xn-1. That is, only the
maintainer of AS1 can create a set with name AS1:AS-FOO; and only the
maintainer of AS1:AS-FOO can create a set with name AS1:AS-FOO:AS-
BAR.
The purpose of an hierarchical set name is to partition the set name
space so that the controllers of the set name X1 controls the whole
set name space under X1, i.e. X1:...:Xn-1. This is important since
anyone can create a set named AS-MCI-CUSTOMERS but only the people
created AS3561 can create AS3561:AS-CUSTOMERS. In the former, it is
not clear if the set AS-MCI-CUSTOMERS has any relationship with MCI.
In the latter, we can guarantee that AS3561:AS-CUSTOMERS and AS3561
are created by the same entity.
6 aut-num Class
ASes are specified using the aut-num class. The attributes of the
aut-num class are shown in Figure 16. The value of the aut-num
attribute is the AS number of the AS described by this object. The
as-name attribute is a symbolic name (in RPSL name syntax) of the AS.
The import, export and default routing policies of the AS are
specified using import, export and default attributes respectively.
Attribute Value Type
aut-num <as-number> mandatory, single-valued, class key
as-name <object-name> mandatory, single-valued
member-of list of <as-set-names> optional, single-valued
import see Section 6.1 optional, multi valued
export see Section 6.2 optional, multi valued
default see Section 6.5 optional, multi valued
Figure 16: aut-num Class Attributes
6.1 import Attribute: Import Policy Specification
Figure 17 shows a typical interconnection of ASes that we will be
using in our examples throughout this section. In this example
topology, there are three ASes, AS1, AS2, and AS3; two exchange
points, EX1 and EX2; and six routers. Routers connected to the same
exchange point peer with each other, i.e. open a connection for
exchanging routing information. Each router would export a subset of
the routes it has to its peer routers. Peer routers would import a
subset of these routes. A router while importing routes would set
some route attributes. For example, AS1 can assign higher preference
values to the routes it imports from AS2 so that it prefers AS2 over
AS3. While exporting routes, a router may also set some route
attributes in order to affect route selection by its peers. For
example, AS2 may set the MULTI-EXIT-DISCRIMINATOR BGP attribute so
that AS1 prefers to use the router 9.9.9.2. Most interAS policies
are specified by specifying what route subsets can be imported or
exported, and how the various BGP route attributes are set and used.
---------------------- ----------------------
7.7.7.1 ------- ------- 7.7.7.2
========
AS1 EX1 ------- 7.7.7.3 AS2
9.9.9.1 ------ ------ 9.9.9.2
---------------------- ----------------------
===========
EX2
----------------------
9.9.9.3 ---------
AS3
----------------------
Figure 17: Example topology consisting of three ASes, AS1, AS2, and
AS3; two exchange points, EX1 and EX2; and six routers.
In RPSL, an import policy is divided into import policy expressions.
Each import policy expression is specified using an import attribute.
The import attribute has the following syntax (we will extend this
syntax later in Sections 6.3 and 6.6):
import: from <peering-1> [action <action-1>]
. . .
from <peering-N> [action <action-N>]
accept <filter>
The action specification is optional. The semantics of an import
attribute is as follows: the set of routes that are matched by
<filter> are imported from all the peers in <peerings>; while
importing routes at <peering-M>, <action-M> is executed.
E.g.
aut-num: AS1
import: from AS2 action pref = 1; accept { 128.9.0.0/16 }
This example states that the route 128.9.0.0/16 is accepted from AS2
with preference 1. In the next few subsections, we will describe how
peerings, actions and filters are specified.
6.1.1 Peering Specification
Our example above used an AS number to specify peerings. The
peerings can be specified at different granularities. The syntax of
a peering specification has two forms. The first one is as follows:
<peer-as> [<peer-router>] [at <local-router>]
where <local-router> and <peer-router> are IP addresses of routers,
<peer-as> is an AS number. <peer-as> must be the AS number of
<peer-router>. Both <local-router> and <peer-router> are optional.
If both <local-router> and <peer-router> are specified, this peering
specification identifies only the peering between these two routers.
If only <local-router> is specified, this peering specification
identifies all the peerings between <local-router> and any of its
peer routers in <peer-as>. If only <peer-router> is specified, this
peering specification identifies all the peerings between any router
in the local AS and <peer-router>. If neither <local-router> nor
<peer-router> is specified, this peering specification identifies all
the peerings between any router in the local AS and any router in
<peer-as>.
We next give examples. Consider the topology of Figure 17 where
7.7.7.1, 7.7.7.2 and 7.7.7.3 peer with each other; 9.9.9.1, 9.9.9.2
and 9.9.9.3 peer with each other. In the following example 7.7.7.1
imports 128.9.0.0/16 from 7.7.7.2.
(1) aut-num: AS1
import: from AS2 7.7.7.2 at 7.7.7.1 accept { 128.9.0.0/16 }
In the following example 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2
and 7.7.7.3.
(2) aut-num: AS1
import: from AS2 at 7.7.7.1 accept { 128.9.0.0/16 }
In the following example 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2
and 7.7.7.3, and 9.9.9.1 imports 128.9.0.0/16 from 9.9.9.2.
(3) aut-num: AS1
import: from AS2 accept { 128.9.0.0/16 }
The second form of <peering> specification has the following syntax:
<as-expression> [at <router-expression>]
where <as-expression> is an expression over AS numbers and sets using
operators AND, OR, and NOT, and <router-expression> is an expression
over router IP addresses and DNS names using operators AND, OR, and
NOT. The DNS name can only be used if there is an inet-rtr object for
that name that binds the name to IP addresses. This form identifies
all the peerings between any local router in <router-expression> to
any of their peer routers in the ASes in <as-expression>. If
<router-expression> is not specified, it defaults to all routers of
the local AS.
In the following example 9.9.9.1 imports 128.9.0.0/16 from 9.9.9.2
and 9.9.9.3.
(4) as-set: AS-FOO
members: AS2, AS3
aut-num: AS1
import: from AS-FOO at 9.9.9.1 accept { 128.9.0.0/16 }
In the following example 9.9.9.1 imports 128.9.0.0/16 from 9.9.9.2
and 9.9.9.3, and 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2 and
7.7.7.3.
(5) aut-num: AS1
import: from AS-FOO accept { 128.9.0.0/16 }
In the following example AS1 imports 128.9.0.0/16 from AS3 at router
9.9.9.1
(6) aut-num: AS1
import: from AS-FOO and not AS2
at not 7.7.7.1
accept { 128.9.0.0/16 }
This is because "AS-FOO and not AS2" equals AS3 and "not 7.7.7.1"
equals 9.9.9.1.
6.1.2 Action Specification
Policy actions in RPSL either set or modify route attributes, such as
assigning a preference to a route, adding a BGP community to the BGP
community path attribute, or setting the MULTI-EXIT-DISCRIMINATOR
attribute. Policy actions can also instruct routers to perform
special operations, such as route flap damping.
The routing policy attributes whose values can be modified in policy
actions are specified in the RPSL dictionary. Please refer to
Section 7 for a list of these attributes. Each action in RPSL is
terminated by the character ';'. It is possible to form composite
policy actions by listing them one after the other. In a composite
policy action, the actions are executed left to right. For example,
aut-num: AS1
import: from AS2
action pref = 10; med = 0; community.append(10250, {3561,10});
accept { 128.9.0.0/16 }
sets pref to 10, med to 0, and then appends 10250 and {3561,10} to
the community path attribute.
6.1.3 Filter Specification
A policy filter is a logical expression which when applied to a set
of routes returns a subset of these routes. We say that the policy
filter matches the subset returned. The policy filter can match
routes using any path attribute, such as the destination address
prefix (or NLRI), AS-path, or community attributes.
The policy filters can be composite by using the operators AND, OR,
and NOT. The following policy filters can be used to select a subset
of routes:
ANY The filter-keyword ANY matches all routes.
Address-Prefix Set This is an explicit list of address prefixes
enclosed in braces '{' and '}'. The policy filter matches the set of
routes whose destination address-prefix is in the set. For example:
{ 0.0.0.0/0 }
{ 128.9.0.0/16, 128.8.0.0/16, 128.7.128.0/17, 5.0.0.0/8 }
{ }
An address prefix can be optionally followed by a range operator
(i.e. '^-', '^+', '^n', or '^n-m'). For example, the set
{ 5.0.0.0/8^+, 128.9.0.0/16^-, 30.0.0.0/8^16, 30.0.0.0/8^24-32 }
contains all the more specifics of 5.0.0.0/8 including 5.0.0.0/8, all
the more specifics of 128.9.0.0/16 excluding 128.9.0.0/16, all the
more specifics of 30.0.0.0/8 which are of length 16 such as
30.9.0.0/16, and all the more specifics of 30.0.0.0/8 which are of
length 24 to 32 such as 30.9.9.96/28.
Route Set Name A route set name matches the set of routes that are
members of the set. A route set name may be a name of a route-set
object, an AS number, or a name of an as-set object (AS numbers and
as-set names implicitly define route sets; please see Section 5.3).
For example:
aut-num: AS1
import: from AS2 action pref = 1; accept AS2
import: from AS2 action pref = 1; accept AS-FOO
import: from AS2 action pref = 1; accept RS-FOO
The keyword PeerAS can be used instead of the AS number of the peer
AS. PeerAS is particularly useful when the peering is specified
using an AS expression. For example:
as-set: AS-FOO
members: AS2, AS3
aut-num: AS1
import: from AS-FOO action pref = 1; accept PeerAS
is same as:
aut-num: AS1
import: from AS2 action pref = 1; accept AS2
import: from AS3 action pref = 1; accept AS3
A route set name can also be followed by one of the operators '^-',
'^+', '^n' or '^n-m'. These operators are distributive over the
route sets. For example, { 5.0.0.0/8, 6.0.0.0/8 }^+ equals {
5.0.0.0/8^+, 6.0.0.0/8^+ }, and AS1^- equals all the exclusive more
specifics of routes originated by AS1.
AS Path Regular Expressions An AS-path regular expression can be used
as a policy filter by enclosing the expression in `<' and `>'. An
AS-path policy filter matches the set of routes which traverses a
sequence of ASes matched by the AS-path regular expression. A router
can check this using the AS_PATH attribute in the Border Gateway
Protocol [18], or the RD_PATH attribute in the Inter-Domain Routing
Protocol[17].
AS-path Regular Expressions are POSIX compliant regular expressions
over the alphabet of AS numbers. The regular expression constructs
are as follows:
ASN where ASN is an AS number. ASN matches the AS-path
that is of length 1 and contains the corresponding AS
number (e.g. AS-path regular expression AS1 matches the
AS-path "1").
The keyword PeerAS can be used instead of the AS number
of the peer AS.
AS-set where AS-set is an AS set name. AS-set matches the AS-paths
that is matched by one of the ASes in the AS-set.
. matches the AS-paths matched by any AS number.
[...] is an AS number set. It matches the AS-paths matched by
the AS numbers listed between the brackets. The AS
numbers in the set are separated by white space
characters. If a `-' is used between two AS numbers in
this set, all AS numbers between the two AS numbers are
included in the set. If an as-set name is listed, all
AS numbers in the as-set are included.
[^...] is a complemented AS number set. It matches any AS-path
which is not matched by the AS numbers in the set.
^ Matches the empty string at the beginning of an AS-path.
$ Matches the empty string at the end of an AS-path.
We next list the regular expression operators in the decreasing order
of evaluation. These operators are left associative, i.e. performed
left to right.
Unary postfix operators * + ? {m} {m,n} {m,}
For a regular expression A, A* matches zero or more
occurrences of A; A+ matches one or more occurrences of
A; A? matches zero or one occurrence of A; A{m} matches
m occurrence of A; A{m,n} matches m to n occurrence of
A; A{m,} matches m or more occurrence of A. For example,
[AS1 AS2]{2} matches AS1 AS1, AS1 AS2, AS2 AS1, and AS2
AS2.
Unary postfix operators ~* ~+ ~{m} ~{m,n} ~{m,}
These operators have similar functionality as the
corresponding operators listed above, but all
occurrences of the regular expression has to match the
same pattern. For example, [AS1 AS2]~{2} matches AS1
AS1 and AS2 AS2, but it does not match AS1 AS2 and AS2
AS1.
Binary catenation operator
This is an implicit operator and exists between two
regular expressions A and B when no other explicit
operator is specified. The resulting expression A B
matches an AS-path if A matches some prefix of the AS-
path and B matches the rest of the AS-path.
Binary alternative (or) operator
For a regular expressions A and B, A B matches any
AS-path that is matched by A or B.
Parenthesis can be used to override the default order of evaluation.
White spaces can be used to increase readability.
The following are examples of AS-path filters:
<AS3>
<^AS1>
<AS2$>
<^AS1 AS2 AS3$>
<^AS1 .* AS2$>.
The first example matches any route whose AS-path contains AS3, the
second matches routes whose AS-path starts with AS1, the third
matches routes whose AS-path ends with AS2, the fourth matches routes
whose AS-path is exactly "1 2 3", and the fifth matches routes whose
AS-path starts with AS1 and ends in AS2 with any number of AS numbers
in between.
Composite Policy Filters The following operators (in decreasing order
of evaluation) can be used to form composite policy filters:
NOT Given a policy filter x, NOT x matches the set of routes that are
not matched by x. That is it is the negation of policy filter x.
AND Given two policy filters x and y, x AND y matches the
intersection of the routes that are matched by x and that are
matched by y.
OR Given two policy filters x and y, x OR y matches the union of
the routes that are matched by x and that are matched by y.
Note that an OR operator can be implicit, that is `x y' is equivalent
to `x OR y'.
E.g.
NOT {128.9.0.0/16, 128.8.0.0/16}
AS226 AS227 OR AS228
AS226 AND NOT {128.9.0.0/16}
AS226 AND {0.0.0.0/0^0-18}
The first example matches any route except 128.9.0.0/16 and
128.8.0.0/16. The second example matches the routes of AS226, AS227
and AS228. The third example matches the routes of AS226 except
128.9.0.0/16. The fourth example matches the routes of AS226 whose
length are not longer than 18.
Routing Policy Attributes Policy filters can also use the values of
other attributes for comparison. The attributes whose values can be
used in policy filters are specified in the RPSL dictionary. Please
refer to Section 7 for details. An example using the the BGP
community attribute is shown below:
aut-num: AS1
export: to AS2 announce AS1 AND NOT community.contains(NO_EXPORT)
Filters using the routing policy attributes defined in the dictionary
are evaluated before evaluating the operators AND, OR and NOT.
6.1.4 Example Policy Expressions
aut-num: AS1
import: from AS2 action pref = 1;
from AS3 action pref = 2;
accept AS4
The above example states that AS4's routes are accepted from AS2 with
preference 1, and from AS3 with preference 2 (routes with lower
integer preference values are preferred over routes with higher
integer preference values).
aut-num: AS1
import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 1;
from AS2 action pref = 2;
accept AS4
The above example states that AS4's routes are accepted from AS2 on
peering 7.7.7.1-7.7.7.2 with preference 1, and on any other peering
with AS2 with preference 2.
6.2 export Attribute: Export Policy Specification
Similarly, an export policy expression is specified using an export
attribute. The export attribute has the following syntax:
export: to <peering-1> [action <action-1>]
. . .
to <peering-N> [action <action-N>]
announce <filter>
The action specification is optional. The semantics of an export
attribute is as follows: the set of routes that are matched by
<filter> are exported to all the peers specified in <peerings>; while
exporting routes at <peering-M>, <action-M> is executed.
E.g.
aut-num: AS1
export: to AS2 action med = 5; community .= 70;
announce AS4
In this example, AS4's routes are announced to AS2 with the med
attribute's value set to 5 and community 70 added to the community
list.
Example:
aut-num: AS1
export: to AS-FOO announce ANY
In this example, AS1 announces all of its routes to the ASes in the
set AS-FOO.
6.3 Other Routing Protocols, Multi-Protocol Routing Protocols, and
Injecting Routes Between Protocols
The more complete syntax of the import and export attributes are as
follows:
import: [protocol <protocol-1>] [into <protocol-2>]
from <peering-1> [action <action-1>]
. . .
from <peering-N> [action <action-N>]
accept <filter>
export: [protocol <protocol-1>] [into <protocol-2>]
to <peering-1> [action <action-1>]
. . .
to <peering-N> [action <action-N>]
announce <filter>
Where the optional protocol specifications can be used for specifying
policies for other routing protocols, or for injecting routes of one
protocol into another protocol, or for multi-protocol routing
policies. The valid protocol names are defined in the dictionary.
The <protocol-1> is the name of the protocol whose routes are being
exchanged. The <protocol-2> is the name of the protocol which is
receiving these routes. Both <protocol-1> and <protocol-2> default
to the Internet Exterior Gateway Protocol, currently BGP.
In the following example, all interAS routes are injected into RIP.
aut-num: AS1
import: from AS2 accept AS2
export: protocol BGP4 into RIP
to AS1 announce ANY
In the following example, AS1 accepts AS2's routes including any more
specifics of AS2's routes, but does not inject these extra more
specific routes into OSPF.
aut-num: AS1
import: from AS2 accept AS2^+
export: protocol BGP4 into OSPF
to AS1 announce AS2
In the following example, AS1 injects its static routes (routes which
are members of the set AS1:RS-STATIC-ROUTES) to the interAS routing
protocol and appends AS1 twice to their AS paths.
aut-num: AS1
import: protocol STATIC into BGP4
from AS1 action ASPath.prepend(AS1, AS1);
accept AS1:RS-STATIC-ROUTES
In the following example, AS1 imports different set of unicast routes
for multicast reverse path forwarding from AS2:
aut-num: AS1
import: from AS2 accept AS2
import: protocol IDMR
from AS2 accept AS2:RS-RPF-ROUTES
6.4 Ambiguity Resolution
It is possible that the same peering can be covered by more that one
peering specification in a policy expression. For example:
aut-num: AS1
import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 2;
from AS2 7.7.7.2 at 7.7.7.1 action pref = 1;
accept AS4
This is not an error, though definitely not desirable. To break the
ambiguity, the action corresponding to the first peering
specification is used. That is the routes are accepted with
preference 2. We call this rule as the specification-order rule.
Consider the example:
aut-num: AS1
import: from AS2 action pref = 2;
from AS2 7.7.7.2 at 7.7.7.1 action pref = 1; dpa = 5;
accept AS4
where both peering specifications cover the peering 7.7.7.1-7.7.7.2,
though the second one covers it more specifically. The specification
order rule still applies, and only the action "pref = 2" is executed.
In fact, the second peering-action pair has no use since the first
peering-action pair always covers it. If the intended policy was to
accept these routes with preference 1 on this particular peering and
with preference 2 in all other peerings, the user should have
specified:
aut-num: AS1
import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 1; dpa = 5;
from AS2 action pref = 2;
accept AS4
It is also possible that more than one policy expression can cover
the same set of routes for the same peering. For example:
aut-num: AS1
import: from AS2 action pref = 2; accept AS4
import: from AS2 action pref = 1; accept AS4
In this case, the specification-order rule is still used. That is,
AS4's routes are accepted from AS2 with preference 2. If the filters
were overlapping but not exactly the same:
aut-num: AS1
import: from AS2 action pref = 2; accept AS4
import: from AS2 action pref = 1; accept AS4 OR AS5
the AS4's routes are accepted from AS2 with preference 2 and however
AS5's routes are also accepted, but with preference 1.
We next give the general specification order rule for the benefit of
the RPSL implementors. Consider two policy expressions:
aut-num: AS1
import: from peerings-1 action action-1 accept filter-1
import: from peerings-2 action action-2 accept filter-2
The above policy expressions are equivalent to the following three
expressions where there is no ambiguity:
aut-num: AS1
import: from peerings-1 action action-1 accept filter-1
import: from peerings-3 action action-2 accept filter-2 AND NOT filter-1
import: from peerings-4 action action-2 accept filter-2
where peerings-3 are those that are covered by both peerings-1 and
peerings-2, and peerings-4 are those that are covered by peerings-2
but not by peerings-1 ("filter-2 AND NOT filter-1" matches the routes
that are matched by filter-2 but not by filter-1).
Example:
aut-num: AS1
import: from AS2 7.7.7.2 at 7.7.7.1
action pref = 2;
accept {128.9.0.0/16}
import: from AS2
action pref = 1;
accept {128.9.0.0/16, 75.0.0.0/8}
Lets consider two peerings with AS2, 7.7.7.1-7.7.7.2 and 9.9.9.1-
9.9.9.2. Both policy expressions cover 7.7.7.1-7.7.7.2. On this
peering, the route 128.9.0.0/16 is accepted with preference 2, and
the route 75.0.0.0/8 is accepted with preference 1. The peering
9.9.9.1-9.9.9.2 is only covered by the second policy expressions.
Hence, both the route 128.9.0.0/16 and the route 75.0.0.0/8 are
accepted with preference 1 on peering 9.9.9.1-9.9.9.2.
Note that the same ambiguity resolution rules also apply to export
and default policy expressions.
6.5 default Attribute: Default Policy Specification
Default routing policies are specified using the default attribute.
The default attribute has the following syntax:
default: to <peering> [action <action>] [networks <filter>]
The <action> and <filter> specifications are optional. The semantics
are as follows: The <peering> specification indicates the AS (and the
router if present) is being defaulted to; the <action> specification,
if present, indicates various attributes of defaulting, for example a
relative preference if multiple defaults are specified; and the
<filter> specifications, if present, is a policy filter. A router
chooses a default router from the routes in its routing table that
matches this <filter>.
In the following example, AS1 defaults to AS2 for routing.
aut-num: AS1
default: to AS2
In the following example, router 7.7.7.1 in AS1 defaults to router
7.7.7.2 in AS2.
aut-num: AS1
default: to AS2 7.7.7.2 at 7.7.7.1
In the following example, AS1 defaults to AS2 and AS3, but prefers
AS2 over AS3.
aut-num: AS1
default: to AS2 action pref = 1;
default: to AS3 action pref = 2;
In the following example, AS1 defaults to AS2 and uses 128.9.0.0/16
as the default network.
aut-num: AS1
default: to AS2 networks { 128.9.0.0/16 }
6.6 Structured Policy Specification
The import and export policies can be structured. We only reccomend
structured policies to advanced RPSL users. Please feel free to skip
this section.
The syntax for a structured policy specification is the following:
<import-factor> ::= from <peering-1> [action <action-1>]
. . .
from <peering-N> [action <action-N>]
accept <filter>;
<import-term> ::= <import-factor>
LEFT-BRACE
<import-factor>
. . .
<import-factor>
RIGHT-BRACE
<import-expression> ::= <import-term>
<import-term> EXCEPT <import-expression>
<import-term> REFINE <import-expression>
import: [protocol <protocol1>] [into <protocol2>]
<import-expression>
Please note the semicolon at the end of an <import-factor>. If the
policy specification is not structured (as in all the examples in
other sections), this semicolon is optional. The syntax and
semantics for an <import-factor> is already defined in Section 6.1.
An <import-term> is either a sequence of <import-factor>'s enclosed
within matching braces (i.e. `{' and `}') or just a single <import-
factor>. The semantics of an <import-term> is the union of <import-
factor>'s using the specification order rule. An <import-expression>
is either a single <import-term> or an <import-term> followed by one
of the keywords "except" and "refine", followed by another <import-
expression>. Note that our definition allows nested expressions.
Hence there can be exceptions to exceptions, refinements to
refinements, or even refinements to exceptions, and so on.
The semantics for the except operator is as follows: The result of an
except operation is another <import-term>. The resulting policy set
contains the policies of the right hand side but their filters are
modified to only include the routes also matched by the left hand
side. The policies of the left hand side are included afterwards and
their filters are modified to exclude the routes matched by the right
hand side. Please note that the filters are modified during this
process but the actions are copied verbatim. When there are multiple
levels of nesting, the operations (both except and refine) are
performed right to left.
Consider the following example:
import: from AS1 action pref = 1; accept as-foo;
except {
from AS2 action pref = 2; accept AS226;
except {
from AS3 action pref = 3; accept {128.9.0.0/16};
}
}
where the route 128.9.0.0/16 is originated by AS226, and AS226 is a
member of the as set as-foo. In this example, the route 128.9.0.0/16
is accepted from AS3, any other route (not 128.9.0.0/16) originated
by AS226 is accepted from AS2, and any other ASes' routes in as-foo
is accepted from AS1.
We can come to the same conclusion using the algebra defined above.
Consider the inner exception specification:
from AS2 action pref = 2; accept AS226;
except {
from AS3 action pref = 3; accept {128.9.0.0/16};
}
is equivalent to
{
from AS3 action pref = 3; accept AS226 AND {128.9.0.0/16};
from AS2 action pref = 2; accept AS226 AND NOT {128.9.0.0/16};
}
Hence, the original expression is equivalent to:
import: from AS1 action pref = 1; accept as-foo;
except {
from AS3 action pref = 3;
accept AS226 AND {128.9.0.0/16};
from AS2 action pref = 2;
accept AS226 AND NOT {128.9.0.0/16};
}
which is equivalent to
import: {
from AS3 action pref = 3;
accept as-foo AND AS226 AND {128.9.0.0/16};
from AS2 action pref = 2;
accept as-foo AND AS226 AND NOT {128.9.0.0/16};
from AS1 action pref = 1;
accept as-foo AND NOT
(AS226 AND NOT {128.9.0.0/16} OR
AS226 AND {128.9.0.0/16});
}
Since AS226 is in as-foo and 128.9.0.0/16 is in AS226, it simplifies to:
import: {
from AS3 action pref = 3; accept {128.9.0.0/16};
from AS2 action pref = 2;
accept AS226 AND NOT {128.9.0.0/16};
from AS1 action pref = 1; accept as-foo AND NOT AS226;
}
In the case of the refine operator, the resulting set is constructed
by taking the cartasian product of the two sides as follows: for each
policy l in the left hand side and for each policy r in the right
hand side, the peerings of the resulting policy are the peerings
common to both r and l; the filter of the resulting policy is the
intersection of l's filter and r's filter; and action of the
resulting policy is l's action followed by r's action. If there are
no common peerings, or if the intersection of filters is empty, a
resulting policy is not generated.
Consider the following example:
import: { from AS-ANY action pref = 1;
accept community.contains({3560,10});
from AS-ANY action pref = 2;
accept community.contains({3560,20});
} refine {
from AS1 accept AS1;
from AS2 accept AS2;
from AS3 accept AS3;
}
Here, any route with community {3560,10} is assigned a preference of
1 and any route with community {3560,20} is assigned a preference of
2 regardless of whom they are imported from. However, only AS1's
routes are imported from AS1, and only AS2's routes are imported from
AS2, and only AS3's routes are imported form AS3, and no routes are
imported from any other AS. We can reach the same conclusion using
the above algebra. That is, our example is equivalent to:
import: {
from AS1 action pref = 1;
accept community.contains({3560,10}) AND AS1;
from AS1 action pref = 2;
accept community.contains({3560,20}) AND AS1;
from AS2 action pref = 1;
accept community.contains({3560,10}) AND AS2;
from AS2 action pref = 2;
accept community.contains({3560,20}) AND AS2;
from AS3 action pref = 1;
accept community.contains({3560,10}) AND AS3;
from AS3 action pref = 2;
accept community.contains({3560,20}) AND AS3;
}
Note that the common peerings between "from AS1" and "from AS-ANY"
are those peerings in "from AS1". Even though we do not formally
define "common peerings", it is straight forward to deduce the
definition from the definitions of peerings (please see Section
6.1.1).
Consider the following example:
import: {
from AS-ANY action med = 0; accept {0.0.0.0/0^0-18};
} refine {
from AS1 at 7.7.7.1 action pref = 1; accept AS1;
from AS1 action pref = 2; accept AS1;
}
where only routes of length 0 to 18 are accepted and med's value is
set to 0 to disable med's effect for all peerings; In addition, from
AS1 only AS1's routes are imported, and AS1's routes imported at
7.7.7.1 are preferred over other peerings. This is equivalent to:
import: {
from AS1 at 7.7.7.1 action med=0; pref=1;
accept {0.0.0.0/0^0-18} AND AS1;
from AS1 action med=0; pref=2; accept {0.0.0.0/0^0-18} AND AS1;
The above syntax and semantics also apply equally to structured
export policies with "from" replaced with "to" and "accept" is
replaced with "announce".
7 dictionary Class
The dictionary class provides extensibility to RPSL. Dictionary
objects define routing policy attributes, types, and routing
protocols. Routing policy attributes, henceforth called rp-
attributes, may correspond to actual protocol attributes, such as the
BGP path attributes (e.g. community, dpa, and AS-path), or they may
correspond to router features (e.g. BGP route flap damping). As new
protocols, new protocol attributes, or new router features are
introduced, the dictionary object is updated to include appropriate
rp-attribute and protocol definitions.
An rp-attribute is an abstract class; that is a data representation
is not available. Instead, they are Accessed through access methods.
For example, the rp-attribute for the BGP AS-path attribute is called
aspath; and it has an access method called prepend which stuffs extra
AS numbers to the AS-path attributes. Access methods can take
arguments. Arguments are strongly typed. For example, the method
prepend above takes AS numbers as argument.
Once an rp-attribute is defined in the dictionary, it can be used to
describe policy filters and actions. Policy analysis tools are
required to fetch the dictionary object and recognize newly defined
rp-attributes, types, and protocols. The analysis tools may
approximate policy analyses on rp-attributes that they do not
understand: a filter method may always match, and an action method
may always perform no-operation. Analysis tools may even download
code to perform appropriate operations using mechanisms outside the
scope of RPSL.
We next describe the syntax and semantics of the dictionary class.
This description is not essential for understanding dictionary
objects (but it is essential for creating one). Please feel free to
skip to the RPSL Initial Dictionary subsection (Section 7.1).
The attributes of the dictionary class are shown in Figure 18. The
dictionary attribute is the name of the dictionary object, obeying
the RPSL naming rules. There can be many dictionary objects, however
there is always one well-known dictionary object "RPSL". All tools
use this dictionary by default.
The rp-attribute attribute has the following syntax:
Attribute Value Type
dictionary <object-name> mandatory, single-valued,
class key
rp-attribute see description in text optional, multi valued
typedef see description in text optional, multi valued
protocol see description in text optional, multi valued
Figure 18: dictionary Class Attributes
rp-attribute: <name>
<method-1>(<type-1-1>, ..., <type-1-N1> [, "..."])
...
<method-M>(<type-M-1>, ..., <type-M-NM> [, "..."])
where <name> is the name of the rp-attribute; and <method-i> is the
name of an access method for the rp-attribute, taking Ni arguments
where the j-th argument is of type <type-i-j>. A method name is
either an RPSL name or one of the operators defined in Figure 19.
The operator methods with the exception of operator() and operator[]
can take only one argument.
operator= operator==
operator<<= operator<
operator>>= operator>
operator+= operator>=
operator-= operator<=
operator*= operator!=
operator/= operator()
operator.= operator[]
Figure 19: Operators
An rp-attribute can have many methods defined for it. Some of the
methods may even have the same name, in which case their arguments
are of different types. If the argument list is followed by "...",
the method takes a variable number of arguments. In this case, the
actual arguments after the Nth argument are of type <type-N>.
Arguments are strongly typed. A type of an argument can be one of
the predefined types or one of the dictionary defined types. The
predefined type names are listed in Figure 20. The integer and the
real types can be followed by a lower and an upper bound to specify
the set of valid values of the argument. The range specification is
optional. We use the ANSI C language conventions for representing
integer, real and string values. The enum type is followed by a list
of RPSL names which are the valid values of the type. The boolean
type can take the values true or false. as_number, ipv4_address,
address_prefix and dns_name types are as in Section 2. filter type
is a policy filter as in Section 6.
integer[lower, upper] as_number
real[lower, upper] ipv4_address
enum[name, name, ...] address_prefix
string address_prefix_range
boolean dns_name
rpsl_word filter
free_text as_set_name
email route_set_name
Figure 20: Predefined Types
The typedef attribute specifies a dictionary defined type. Its
syntax is as follows:
typedef: <name> union <type-1>, ... , <type-N>
<name> list [<min_elems>:<max_elems>] of <type>
where <name> is the name of the type being defined and <type-M> is
another type name, either predefined or dictionary defined. In the
first form, the type defined is either of the types <type-1> through
<type-N> (analogous to unions in C[12]). In the second form, the
type defined is a list type where the list elements are of <type> and
the list contains at least <min_elems> and at most <max_elems>
elements. The size specification is optional. In this case, there
is no restriction in the number of list elements. A value of a list
type is represented as a sequence of elements separated by the
character "," and enclosed by the characters "{" and "}".
A protocol attribute of the dictionary class defines a protocol and a
set of peering options for that protocol (which are used in inet-rtr
class in Section 9). Its syntax is as follows:
protocol: <name>
MANDATORY OPTIONAL <option-1>(<type-1-1>, ...,
<type-1-N1> [, "..."])
...
MANDATORY OPTIONAL <option-M>(<type-M-1>, ...,
<type-M-NM> [, "..."])
where <name> is the name of the protocol; MANDATORY and OPTIONAL are
keywords; and <option-i> is a peering option for this protocol,
taking Ni many arguments. The syntax and semantics of the arguments
are as in the rp-attribute. If the keyword MANDATORY is used the
option is mandatory and needs to be specified for each peering of
this protocol. If the keyword OPTIONAL is used the option can be
skipped.
7.1 Initial RPSL Dictionary and Example Policy Actions and Filters
dictionary: RPSL
rp-attribute: # preference, smaller values represent higher preferences
pref
operator=(integer[0, 65535])
rp-attribute: # BGP multi_exit_discriminator attribute
med
operator=(integer[0, 65535])
# to set med to the IGP metric: med = igp_cost;
operator=(enum[igp_cost])
rp-attribute: # BGP destination preference attribute (dpa)
dpa
operator=(integer[0, 65535])
rp-attribute: # BGP aspath attribute
aspath
# prepends AS numbers from last to first order
prepend(as_number, ...)
typedef: # a community value in RPSL is either
# - a 4 byte integer
# - internet, no_export, no_advertise (see RFC-1997)
# - two 2-byte integers to be concatanated eg. {3561,70}
community_elm union
integer[1, 4294967200],
enum[internet, no_export, no_advertise],
list[2:2] of integer[0, 65535]
typedef: # list of community values { 40, no_export, {3561,70}}
community_list
list of community_elm
rp-attribute: # BGP community attribute
community
# set to a list of communities
operator=(community_list)
# order independent equality comparison
operator==(community_list)
# append community values
operator.=(community_elm)
append(community_elm, ...)
# delete community values
delete(community_elm, ...)
# a filter: true if one of community values is contained
contains(community_elm, ...)
# shortcut to contains: community(no_export, {3561,70})
operator()(community_elm, ...)
rp-attribute: # next hop router in a static route
next-hop
operator=(ipv4_address) # a router address
operator=(enum[self]) # router's own address
rp-attribute: # cost of a static route
cost
operator=(integer[0, 65535])
protocol: BGP4
# as number of the peer router
MANDATORY asno(as_number)
# enable flap damping
OPTIONAL flap_damp()
OPTIONAL flap_damp(integer[0,65535],# penalty per flap
integer[0,65535],
# penalty value for supression
integer[0,65535],# penalty value for reuse
integer[0,65535],# halflife in secs when up
integer[0,65535],
# halflife in secs when down
integer[0,65535])# maximum penalty
protocol: OSPF
protocol: RIP
protocol: IGRP
protocol: IS-IS
protocol: STATIC
protocol: RIPng
protocol: DVMRP
protocol: PIM-DM
protocol: PIM-SM
protocol: CBT
protocol: MOSPF
Figure 21: RPSL Dictionary
Figure 21 shows the initial RPSL dictionary. It has seven rp-
attributes: pref to assign local preference to the routes accepted;
med to assign a value to the MULTI_EXIT_DISCRIMINATOR BGP attribute;
dpa to assign a value to the DPA BGP attribute; aspath to prepend a
value to the AS_PATH BGP attribute; community to assign a value to or
to check the value of the community BGP attribute; next-hop to assign
next hop routers to static routes; and cost to assign a cost to
static routes. The dictionary defines two types: community_elm and
community_list. community_elm type is either a 4-byte unsigned
integer, or one of the keywords no_export or no_advertise (defined in
[7]), or a list of two 2-byte unsigned integers in which case the two
integers are concatenated to form a 4-byte integer. (The last form
is often used in the Internet to partition the community number
space. A provider uses its AS number as the first two bytes, and
assigns a semantics of its choice to the last two bytes.)
The initial dictionary (Figure 21) defines only options for the
Border Gateway Protocol: asno and flap_damp. The mandatory asno
option is the AS number of the peer router. The optional flap_damp
option instructs the router to damp route flaps[19] when importing
routes from the peer router.
It can be specified with or without parameters. If parameters are
missing, they default to:
flap_damp(1000, 2000, 750, 900, 900, 20000)
That is, a penalty of 1000 is assigned at each route flap, the route
is suppressed when penalty reaches 2000. The penalty is reduced in
half after 15 minutes (900 seconds) of stability regardless of
whether the route is up or down. A supressed route is reused when
the penalty falls below 750. The maximum penalty a route can be
assigned is 20,000 (i.e. the maximum suppress time after a route
becomes stable is about 75 minutes). These parameters are consistent
with the default flap damping parameters in several routers.
Policy Actions and Filters Using RP-Attributes
The syntax of a policy action or a filter using an rp-attribute x is
as follows:
x.method(arguments)
x "op" argument
where method is a method and "op" is an operator method of the rp-
attribute x. If an operator method is used in specifying a composite
policy filter, it evaluates earlier than the composite policy filter
operators (i.e. AND, OR, NOT, and implicit or operator).
The pref rp-attribute can be assigned a positive integer as follows:
pref = 10;
The med rp-attribute can be assigned either a positive integer or the
word "igp_cost" as follows:
med = 0;
med = igp_cost;
The dpa rp-attribute can be assigned a positive integer as follows:
dpa = 100;
The BGP community attribute is list-valued, that is it is a list of
4-byte integers each representing a "community". The following
examples demonstrate how to add communities to this rp-attribute:
community .= 100;
community .= NO_EXPORT;
community .= {3561,10};
In the last case, a 4-byte integer is constructed where the more
significant two bytes equal 3561 and the less significant two bytes
equal 10. The following examples demonstrate how to delete
communities from the community rp-attribute:
community.delete(100, NO_EXPORT, {3561,10});
Filters that use the community rp-attribute can be defined as
demonstrated by the following examples:
community.contains(100, NO_EXPORT, {3561,10});
community(100, NO_EXPORT, {3561,10}); # shortcut
The community rp-attribute can be set to a list of communities as
follows:
community = {100, NO_EXPORT, {3561,10}, 200};
community = {};
In this first case, the community rp-attribute contains the
communities 100, NO_EXPORT, {3561,10}, and 200. In the latter case,
the community rp-attribute is cleared. The community rp-attribute
can be compared against a list of communities as follows:
community == {100, NO_EXPORT, {3561,10}, 200}; # exact match
To influence the route selection, the BGP as_path rp-attribute can be
made longer by prepending AS numbers to it as follows:
aspath.prepend(AS1);
aspath.prepend(AS1, AS1, AS1);
The following examples are invalid:
med = -50; # -50 is not in the range
med = igp; # igp is not one of the enum values
med.assign(10); # method assign is not defined
community.append({AS3561,20}); # the first argument should be 3561
Figure 22 shows a more advanced example using the rp-attribute
community. In this example, AS3561 bases its route selection
preference on the community attribute. Other ASes may indirectly
affect AS3561's route selection by including the appropriate
communities in their route announcements.
aut-num: AS1
export: to AS2 action community.={3561,90};
to AS3 action community.={3561,80};
announce AS1
as-set: AS3561:AS-PEERS
members: AS2, AS3
aut-num: AS3561
import: from AS3561:AS-PEERS
action pref = 10;
accept community.contains({3561,90})
import: from AS3561:AS-PEERS
action pref = 20;
accept community.contains({3561,80})
import: from AS3561:AS-PEERS
action pref = 20;
accept community.contains({3561,70})
import: from AS3561:AS-PEERS
action pref = 0;
accept ANY
Figure 22: Policy example using the community rp-attribute.
8 Advanced route Class
8.1 Specifying Aggregate Routes
The components, aggr-bndry, aggr-mtd, export-comps, inject, and holes
attributes are used for specifying aggregate routes [9]. A route
object specifies an aggregate route if any of these attributes, with
the exception of inject, is specified. The origin attribute for an
aggregate route is the AS performing the aggregation, i.e. the
aggregator AS. In this section, we used the term "aggregate" to refer
to the route generated, the term "component" to refer to the routes
used to generate the path attributes of the aggregate, and the term
"more specifics" to refer to any route which is a more specific of
the aggregate regardless of whether it was used to form the path
attributes.
The components attribute defines what component routes are used to
form the aggregate. Its syntax is as follows:
components: [ATOMIC] [[protocol <protocol>] <filter>
[protocol <protocol> <filter> ...]]
where <protocol> is a routing protocol name such as BGP, OSPF or RIP
(valid names are defined in the dictionary) and <filter> is a policy
expression. The routes that match one of these filters and are
learned from the corresponding protocol are used to form the
aggregate. If <protocol> is omitted, it defaults to any protocol.
<filter> implicitly contains an "AND" term with the more specifics of
the aggregate so that only the component routes are selected. If the
keyword ATOMIC is used, the aggregation is done atomically [9]. If a
<filter> is not specified it defaults to more specifics. If the
components attribute is missing, all more specifics without the
ATOMIC keyword is used.
route: 128.8.0.0/15
origin: AS1
components: <^AS2>
route: 128.8.0.0/15
origin: AS1
components: protocol BGP {128.8.0.0/16^+}
protocol OSPF {128.9.0.0/16^+}
Figure 23: Two aggregate route objects.
Figure 23 shows two route objects. In the first example, more
specifics of 128.8.0.0/15 with AS paths starting with AS2 are
aggregated. In the second example, some routes learned from BGP and
some routes learned form OSPF are aggregated.
The aggr-bndry attribute is an expression over AS numbers and sets
using operators AND, OR, and NOT. The result defines the set of ASes
which form the aggregation boundary. If the aggr-bndry attribute is
missing, the origin AS is the sole aggregation boundary. Outside the
aggregation boundary, only the aggregate is exported and more
specifics are suppressed. However, within the boundary, the more
specifics are also exchanged.
The aggr-mtd attribute specifies how the aggregate is generated. Its
syntax is as follow:
aggr-mtd: inbound
outbound [<as-expression>]
where <as-expression> is an expression over AS numbers and sets using
operators AND, OR, and NOT. If <as-expression> is missing, it
defaults to AS-ANY. If outbound aggregation is specified, the more
specifics of the aggregate will be present within the AS and the
aggregate will be formed at all inter-AS boundaries with ASes in
<as-expression> before export, except for ASes that are within the
aggregating boundary (i.e. aggr-bndry is enforced regardless of
<as-expression>). If inbound aggregation is specified, the aggregate
is formed at all inter-AS boundaries prior to importing routes into
the aggregator AS. Note that <as-expression> can not be specified
with inbound aggregation. If aggr-mtd attribute is missing, it
defaults to "outbound AS-ANY".
route: 128.8.0.0/15 route: 128.8.0.0/15
origin: AS1 origin: AS2
components: {128.8.0.0/15^-} components: {128.8.0.0/15^-}
aggr-bndry: AS1 OR AS2 aggr-bndry: AS1 OR AS2
aggr-mtd: outbound AS-ANY aggr-mtd: outbound AS-ANY
Figure 24: Outbound multi-AS aggregation example.
Figure 24 shows an example of an outbound aggregation. In this
example, AS1 and AS2 are coordinating aggregation and announcing only
the less specific 128.8.0.0/15 to outside world, but exchanging more
specifics between each other. This form of aggregation is useful
when some of the components are within AS1 and some are within AS2.
When a set of routes are aggregated, the intent is to export only the
aggregate route and suppress exporting of the more specifics outside
the aggregation boundary. However, to satisfy certain policy and
topology constraints (e.g. a multi-homed component), it is often
required to export some of the components. The export-comps
attribute equals an RPSL filter that matches the more specifics that
need to be exported outside the aggregation boundary. If this
attribute is missing, more specifics are not exported outside the
aggregation boundary. Note that, the export-comps filter contains an
implicit "AND" term with the more specifics of the aggregate.
Figure 25 shows an example of an outbound aggregation. In this
example, the more specific 128.8.8.0/24 is exported outside AS1 in
addition to the aggregate. This is useful, when 128.8.8.0/24 is
multi-homed site to AS1 with some other AS.
route: 128.8.0.0/15
origin: AS1
components: {128.8.0.0/15^-}
aggr-mtd: outbound AS-ANY
export-comps: {128.8.8.0/24}
Figure 25: Outbound aggregation with export exception.
The inject attribute specifies which routers perform the aggregation
and when they perform it. Its syntax is as follow:
inject: [at <router-expression>] ...
[action <action>]
[upon <condition>]
where <action> is an action specification (see Section 6.1.2),
<condition> is a boolean expression described below, and<router-
expression> is an expression over router IP addresses and DNS names
using operators AND, OR, and NOT. The DNS name can only be used if
there is an inet-rtr object for that name that binds the name to IP
addresses.
All routers in <router-expression> and in the aggregator AS perform
the aggregation. If a <router-expression> is not specified, all
routers inside the aggregator AS perform the aggregation. The
<action> specification may set path attributes of the aggregate, such
as assign a preferences to the aggregate.
The upon clause is a boolean condition. The aggregate is generated
if and only if this condition is true. <condition> is a boolean
expression using the logical operators AND and OR (i.e. operator NOT
is not allowed) over:
HAVE-COMPONENTS { list of prefixes }
EXCLUDE { list of prefixes }
STATIC
The list of prefixes in HAVE-COMPONENTS can only be more specifics of
the aggregate. It evaluates to true when all the prefixes listed are
present in the routing table of the aggregating router. The list can
also include prefix ranges (i.e. using operators ^-, ^+, ^n, and ^n-
m). In this case, at least one prefix from each prefix range needs
to be present in the routing table for the condition to be true. The
list of prefixes in EXCLUDE can be arbitrary. It evaluates to true
when none of the prefixes listed is present in the routing table.
The list can also include prefix ranges, and no prefix in that range
should be present in the routing table. The keyword static always
evaluates to true. If no upon clause is specified the aggregate is
generated if an only if there is a component in the routing table
(i.e. a more specific that matches the filter in the components
attribute).
route: 128.8.0.0/15
origin: AS1
components: {128.8.0.0/15^-}
aggr-mtd: outbound AS-ANY
inject: at 1.1.1.1 action dpa = 100;
inject: at 1.1.1.2 action dpa = 110;
route: 128.8.0.0/15
origin: AS1
components: {128.8.0.0/15^-}
aggr-mtd: outbound AS-ANY
inject: upon HAVE-COMPONENTS {128.8.0.0/16, 128.9.0.0/16}
holes: 128.8.8.0/24
Figure 26: Examples of inject.
Figure 26 shows two examples. In the first case, the aggregate is
injected at two routers each one setting the dpa path attribute
differently. In the second case, the aggregate is generated only if
both 128.8.0.0/16 and 128.9.0.0/16 are present in the routing table,
as opposed to the first case where the presence of just one of them
is sufficient for injection.
The holes attribute lists the component address prefixes which are
not reachable through the aggregate route (perhaps that part of the
address space is unallocated). The holes attribute is useful for
diagnosis purposes. In Figure 26, the second example has a hole,
namely 128.8.8.0/24. This may be due to a customer changing
providers and taking this part of the address space with it.
8.1.1 Interaction with policies in aut-num class
An aggregate formed is announced to other ASes only if the export
policies of the AS allows exporting the aggregate. When the
aggregate is formed, the more specifics are suppressed from being
exported except to the ASes in aggr-bndry and except the components
in export-comps. For such exceptions to happen, the export policies
of the AS should explicitly allow exporting of these exceptions.
If an aggregate is not formed (due to the upon clause), then the more
specifics of the aggregate can be exported to other ASes, but only if
the export policies of the AS allows it. In other words, before a
route (aggregate or more specific) is exported it is filtered twice,
once based on the route objects, and once based on the export
policies of the AS.
route: 128.8.0.0/16
origin: AS1
route: 128.9.0.0/16
origin: AS1
route: 128.8.0.0/15
origin: AS1
aggr-bndry: AS1 or AS2 or AS3
aggr-mtd: outbound AS3 or AS4 or AS5
components: {128.8.0.0/16, 128.9.0.0/16}
inject: upon HAVE-COMPONENTS {128.9.0.0/16, 128.8.0.0/16}
aut-num: AS1
export: to AS2 announce AS1
export: to AS3 announce AS1 and not {128.9.0.0/16}
export: to AS4 announce AS1
export: to AS5 announce AS1
export: to AS6 announce AS1
Figure 27: Interaction with policies in aut-num class.
In Figure 27 shows an interaction example. By examining the route
objects, the more specifics 128.8.0.0/16 and 128.9.0.0/16 should be
exchanged between AS1, AS2 and AS3 (i.e. the aggregation boundary).
Outbound aggregation is done to AS4 and AS5 and not to AS3, since AS3
is in the aggregation boundary. The aut-num object allows exporting
both components to AS2, but only the component 128.8.0.0/16 to AS3.
The aggregate can only be formed if both components are available.
In this case, only the aggregate is announced to AS4 and AS5.
However, if one of the components is not available the aggregate will
not be formed, and any available component or more specific will be
exported to AS4 and AS5. Regardless of aggregation is performed or
not, only the more specifics will be exported to AS6 (it is not
listed in the aggr-mtd attribute).
When doing an inbound aggregation, configuration generators may
eliminating the aggregation statements on routers where import policy
of the AS prohibits importing of any more specifics.
8.1.2 Ambiguity resolution with overlapping aggregates
When several aggregate routes are specified and they overlap, i.e.
one is less specific of the other, they must be evaluated more
specific to less specific order. When an aggregation is performed,
the aggregate and the components listed in the export-comps attribute
are available for generating the next less specific aggregate. The
components that are not specified in the export-comps attribute are
not available. A route is exportable to an AS if it is the least
specific aggregate exportable to that AS or it is listed in the
export-comps attribute of an exportable route. Note that this is a
recursive definition.
route: 128.8.0.0/15
origin: AS1
aggr-bndry: AS1 or AS2
aggr-mtd: outbound
inject: upon HAVE-COMPONENTS {128.8.0.0/16, 128.9.0.0/16}
route: 128.10.0.0/15
origin: AS1
aggr-bndry: AS1 or AS3
aggr-mtd: outbound
inject: upon HAVE-COMPONENTS {128.10.0.0/16, 128.11.0.0/16}
export-comps: {128.11.0.0/16}
route: 128.8.0.0/14
origin: AS1
aggr-bndry: AS1 or AS2 or AS3
aggr-mtd: outbound
inject: upon HAVE-COMPONENTS {128.8.0.0/15, 128.10.0.0/15}
export-comps: {128.10.0.0/15}
Figure 28: Overlapping aggregations.
In Figure 28, AS1 together with AS2 aggregates 128.8.0.0/16 and
128.9.0.0/16 into 128.8.0.0/15. Together with AS3, AS1 aggregates
128.10.0.0/16 and 128.11.0.0/16 into 128.10.0.0/15. But altogether
they aggregate these four routes into 128.8.0.0/14. Assuming all
four components are available, a router in AS1 for an outside AS, say
AS4, will first generate 128.8.0.0/15 and 128.10.0.0/15. This will
make 128.8.0.0/15, 128.10.0.0/15 and its exception 128.11.0.0/16
available for generating 128.8.0.0/14. The router will then generate
128.8.0.0/14 from these three routes. Hence for AS4, 128.8.0.0/14
and its exception 128.10.0.0/15 and its exception 128.11.0.0/16 will
be exportable.
For AS2, a router in AS1 will only generate 128.10.0.0/15. Hence,
128.10.0.0/15 and its exception 128.11.0.0/16 will be exportable.
Note that 128.8.0.0/16 and 128.9.0.0/16 are also exportable since
they did not participate in an aggregate exportable to AS2.
Similarly, for AS3, a router in AS1 will only generate 128.8.0.0/15.
In this case 128.8.0.0/15, 128.10.0.0/16, 128.11.0.0/16 are
exportable.
8.2 Specifying Static Routes
The inject attribute can be used to specify static routes by using
"upon static" as the condition:
inject: [at <router>] ...
[action <action>]
upon static
In this case, the <router> executes the <action> and injects the
route to the interAS routing system statically. <action> may set
certain route attributes such as a next-hop router or a cost.
In the following example, the router 7.7.7.1 injects the route
128.7.0.0/16. The next-hop routers (in this example, there are two
next-hop routers) for this route are 7.7.7.2 and 7.7.7.3 and the
route has a cost of 10 over 7.7.7.2 and 20 over 7.7.7.3.
route: 128.7.0.0/16
origin: AS1
inject: at 7.7.7.1 action next-hop = 7.7.7.2; cost = 10; upon static
inject: at 7.7.7.1 action next-hop = 7.7.7.3; cost = 20; upon static
9 inet-rtr Class
Routers are specified using the inet-rtr class. The attributes of
the inet-rtr class are shown in Figure 29. The inet-rtr attribute is
a valid DNS name of the router described. Each alias attribute, if
present, is a canonical DNS name for the router. The local-as
attribute specifies the AS number of the AS which owns/operates this
router.
Attribute Value Type
inet-rtr <dns-name> mandatory, single-valued,
class key
alias <dns-name> optional, multi-valued
local-as <as-number> mandatory, single-valued
ifaddr see description in text mandatory, multi-valued
peer see description in text optional, multi-valued
Figure 29: inet-rtr Class Attributes
The value of an ifaddr attribute has the following syntax:
<ipv4-address> masklen <integer> [action <action>]
The IP address and the mask length are mandatory for each interface.
Optionally an action can be specified to set other parameters of this
interface.
Figure 30 presents an example inet-rtr object. The name of the
router is "amsterdam.ripe.net". "amsterdam1.ripe.net" is a canonical
name for the router. The router is connected to 4 networks. Its IP
addresses and mask lengths in those networks are specified in the
ifaddr attributes.
inet-rtr: Amsterdam.ripe.net
alias: amsterdam1.ripe.net
local-as: AS3333
ifaddr: 192.87.45.190 masklen 24
ifaddr: 192.87.4.28 masklen 24
ifaddr: 193.0.0.222 masklen 27
ifaddr: 193.0.0.158 masklen 27
peer: BGP4 192.87.45.195 asno(AS3334), flap_damp()
Figure 30: inet-rtr Objects
Each peer attribute, if present, specifies a protocol peering with
another router. The value of a peer attribute has the following
syntax:
<protocol> <ipv4-address> <options>
where <protocol> is a protocol name, <ipv4-address> is the IP address
of the peer router, and <options> is a comma separated list of
peering options for <protocol>. Possible protocol names and
attributes are defined in the dictionary (please see Section 7). In
the above example, the router has a BGP peering with the router
192.87.45.195 in AS3334 and turns the flap damping on when importing
routes from this router.
10 Security Considerations
This document describes RPSL, a language for expressing routing
policies. The language defines a maintainer (mntner class) object
which is the entity which controls or "maintains" the objects stored
in a database expressed by RPSL. Requests from maintainers can be
authenticated with various techniques as defined by the "auth"
attribute of the maintainer object.
The exact protocols used by IRR's to communicate RPSL objects is
beyond the scope of this document, but it is envisioned that several
techniques may be used, ranging from interactive query/update
protocols to store and forward protocols similar to or based on
electronic mail (or even voice telephone calls). Regardless of which
protocols are used in a given situation, it is expected that
appropriate security techniques such as IPSEC, TLS or PGP/MIME will
be utilized.
11 Acknowledgements
We would like to thank Jessica Yu, Randy Bush, Alan Barrett, David
Kessens, Bill Manning, Sue Hares, Ramesh Govindan, Kannan Varadhan,
Satish Kumar, Craig Labovitz, Rusty Eddy, David J. LeRoy, David
Whipple, Jon Postel, Deborah Estrin, Elliot Schwartz, Joachim
Schmitz, Mark Prior, Tony Przygienda, David Woodgate, and the
participants of the IETF RPS Working Group for various comments and
suggestions.
References
[1] Internet Routing Registry. Procedures.
http://www.ra.net/RADB.tools.docs/,
http://www.ripe.net/db/doc.Html.
[2] Alaettinouglu, C., Meyer, D., and J. Schmitz, "Application of
Routing Policy Specification Language (RPSL) on the Internet",
Work in Progress.
[3] T. Bates. Specifying an `Internet Router' in the Routing
Registry. Technical Report RIPE-122, RIPE, RIPE NCC, Amsterdam,
Netherlands, October 1994.
[4] T. Bates, E. Gerich, L. Joncheray, J-M. Jouanigot, D.
Karrenberg, M. Terpstra, and J. Yu. Representation of IP
Routing Policies in a Routing Registry. Technical Report ripe-
181, RIPE, RIPE NCC, Amsterdam, Netherlands, October 1994.
[5] Bates, T., Gerich, E., Joncheray, L., Jouanigot, J.M.,
Karrenberg, D., Terpstra, M., and J. Yu, "Representation of IP
Routing Policies in a Routing Registry," RFC1786, March 1995.
[6] T. Bates, J-M. Jouanigot, D. Karrenberg, P. Lothberg, and
M. Terpstra. Representation of IP Routing Policies in the RIPE
Database. Technical Report ripe-81, RIPE, RIPE NCC, Amsterdam,
Netherlands, February 1993.
[7] Chandra, R., Traina, P., and T. Li, "BGP Communities Attribute,"
RFC1997, August 1996.
[8] Crocker, D., "Standard for the format of ARPA Internet text
messages, STD 11, RFC822, August 1982.
[9] V. Fuller, T. Li, J. Yu, and K. Varadhan. Classless Inter-
Domain Routing (CIDR): an Address Assignment and Aggregation
Strategy, 1993.
[10] D. Karrenberg and T. Bates. Description of Inter-AS Networks
in the RIPE Routing Registry. Technical Report RIPE-104, RIPE,
RIPE NCC, Amsterdam, Netherlands, December 1993.
[11] D. Karrenberg and M. Terpstra. Authorisation and
Notification of Changes in the RIPE Database. Technical Report
ripe-120, RIPE, RIPE NCC, Amsterdam, Netherlands, October 1994.
[12] B. W. Kernighan and D. M. Ritchie. The C Programming
Language. Prentice-Hall, 1978.
[13] Kessens, D., Woeber, W., and D. Conrad, "RIDE referencing",
Work in Progress.
[14] A. Lord and M. Terpstra. RIPE Database Template for
Networks and Persons. Technical Report ripe-119, RIPE, RIPE
NCC, Amsterdam, Netherlands, October 1994.
[15] A. M. R. Magee. RIPE NCC Database Documentation. Technical
Report RIPE-157, RIPE, RIPE NCC, Amsterdam, Netherlands, May
1997.
[16] Mockapetris, P., "Domain names - concepts and facilities,"
STD 13, RFC1034, November 1987.
[17] Y. Rekhter. Inter-Domain Routing Protocol (IDRP). Journal
of Internetworking Research and Experience, 4:61--80, 1993.
[18] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP-4),"
RFC1771, March 1995.
[19] Villamizar, C., Chandra, R., and R. Govindan, "BGP Route
Flap Damping", Work in Progress.
A Routing Registry Sites
The set of routing registries as of November 1996 are RIPE, RADB,
CANet, MCI and ANS. You may contact one of these registries to find
out the current list of registries.
B Authors' Addresses
Cengiz Alaettinoglu
USC Information Sciences Institute
4676 Admiralty Way, Suite 1001
Marina del Rey, CA 90292
EMail: cengiz@isi.edu
Tony Bates
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
EMail: tbates@cisco.com
Elise Gerich
At Home Network
385 Ravendale Drive
Mountain View, CA 94043
EMail: epg@home.net
Daniel Karrenberg
RIPE Network Coordination Centre (NCC)
Kruislaan 409
NL-1098 SJ Amsterdam
Netherlands
EMail: dfk@ripe.net
David Meyer
University of Oregon
Eugene, OR 97403
EMail: meyer@antc.uoregon.edu
Marten Terpstra
c/o Bay Networks, Inc.
2 Federal St
Billerica MA 01821
EMail: marten@BayNetworks.com
Curtis Villamizar
ANS
EMail: curtis@ans.net
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