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RFC2335 - A Distributed NHRP Service Using SCSP

王朝other·作者佚名  2008-05-31
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Network Working Group J. LUCiani

Request for Comments: 2335 Bay Networks

Category: Standards Track April 1998

A Distributed NHRP Service Using SCSP

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.

Abstract

This document describes a method for distributing an NHRP service

within a LIS [1]. This method uses the Server Cache Synchronization

Protocol (SCSP) [2] to synchronize the client information databases

held by NHRP Servers (NHSs) within a LIS.

1. Introduction

The keyWords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,

SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this

document, are to be interpreted as described in [4].

NHRP Clients (NHCs) register their existence and reachability

information with NHRP Servers (NHSs). There may be multiple NHSs in

a given Logical IP Subnet (LIS). NHCs do not necessarily register

with all NHSs in a LIS; however, all NHCs need to be able to query at

least one NHS about any NHC within the LIS. Thus, the contents of

the NHS databases in a LIS need to be synchronized across the LIS.

The Server Cache Synchronization Protocol (SCSP) solves the

generalized server synchronization/cache-replication problem for

distributed databases and thus SCSP may be applied to the NHS

database synchronization problem within the LIS.

SCSP is defined in two parts: the protocol independent part and the

client/server protocol specific part. The protocol independent part

is defined in [2] whereas this document will specify the

client/server protocol specific part where NHRP is the client/server

protocol.

This document is separate from [2] because it was felt that it was

desirable to allow the client/server protocol specific part

specification for NHRP to progress independently from the protocol

independent specification.

2. Overview

All NHSs belonging to a Logical IP Subnet (LIS) [1] are said to

belong to a Server Group (SG). An SG is identified by, not

surprisingly, its SGID which is contained in a field in all SCSP

packets. All SCSP packets contain a Protocol ID (PID) field as well.

This PID field is set to 0x0002 to signify that SCSP synchronizing

NHS databases as opposed to synchronizing some other protocol's

databases (see Section B.2.0.1 of [2] for more details). In general,

PIDs for SCSP will be assigned by IANA as described in Section C of

[2]. In the case of NHRP, the client/server protocol specific

specification was initially written at the same time as SCSP, and

thus a PID=0x0002 was assigned by the author.

SCSP places no topological requirements upon an NHRP SG. Obviously,

however, the resultant graph of NHSs must span the set of NHSs to be

synchronized. For more information about the client/server protocol

independent part of SCSP, the reader is encouraged to see [2].

When a SG is using SCSP for synchronization, an NHC will register

with only one NHS, but the NHC MAY use any NHS in the SG. When an

NHC wishes to leave a SG, the NHC MUST do one of the following: 1)

the NHC MUST send an NHRP Purge Request for itself requesting a

reply, and it MUST wait for an NHRP Purge Reply, 2) the NHC MUST keep

the Request ID it used when registering itself in non-volatile RAM

and use a Request ID larger than the one saved when re-registering,

or 3) the NHC MUST not re-register for a time equal to the Holding

Time specified in the previous registration. It is necessary to do

one of the previous in order to prevent the unlikely case of race

conditions from occurring during updated. In the case where method 2

is used, the NHS with which the NHC registered uses its ID as the OID

and the Request ID from the NHC as the CSA Sequence Number in the

CSA(S) Record.

3. Format of the CSA Record NHRP Specific Part

CSA Records in SCSP contain a "Client/Server Protocol Specific Part"

which contains the non-protocol independent information for a given

server's cache entry.

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Address Family Number NHRP Protocol Type

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Snap

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Snap NHRP Vers Num Flags

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Request ID

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

State Prefix Length unused

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Maximum Transmission Unit Holding Time

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Cli Addr T/L Cli SAddr T/L Cli Proto Len Preference

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Client Subnetwork Address (variable length)

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Client Subnetwork Subaddress (variable length)

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Client Protocol Address (variable length)

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The following six fields contain values specified in the common

header of the mandatory part of an NHRP Registration Request or NHRP

Purge Request packet which caused the

creation/deletion/modification/update/etc. of an NHS's cache entry.

Address Family Number

Defines the type of "link layer" addresses being carried. This

number is taken from the 'address family number' list specified in

[3]. This field is the same field which would be supplied in an

NHRP packet in the ar$afn field.

NHRP Protocol Type

This field is the same field which would be supplied in an NHRP

packet in the ar$pro.type field.

Snap

This field is the same field which would be supplied in an NHRP

packet in the ar$pro.snap field.

NHRP Vers Num

This field indicates what version of generic address mapping and

management protocol that is represented by this message. This

field contains 0x01 for the NHRP protocol version 1. This field is

the same field which would be supplied in an NHRP packet in the

ar$op.version field.

Flags

Defined flags are as follows:

0 1

0 1

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

UA unused

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

U

This is the Uniqueness bit.

A

When set, this bit specifies that the cache entry was created

as a result of ATMARP client interaction with the NHS.

Request ID

This field contains the Request ID value placed in the cache entry

of the NHS as a result of an NHRP Registration Request. This NHS

is the NHS causing a synchronization event.

State

This field contains a value which represents the new state of the

client.

0 - Client is registered and available.

1 - Client reregistered.

2 - Client has been purged.

3 - No such client data in server cache

Note that a time-out of a cache entry does not cause a CSA Record

to be sent because, if everything is working properly then all NHSs

have the cache entry timing out at the same time. Thus, the

individual NHSs would take the appropriate actions necessary.

The following ten fields contain values specified in or derived from

the CIE of an NHRP Registration Request or NHRP Purge Request packet

which caused the creation/deletion/modification/update/etc. of an

NHS's cache entry.

Prefix Length

This field contains the internetwork layer address prefix length

value covered by the cache entry being synchronized.

Maximum Transmission Unit

This field contains a value supplied by or derived from information

in the CIE of the NHRP Registration Request packet.

Holding Time

The Holding Time field specifies the number of seconds remaining

for which the Next Hop NBMA information specified in the CIE of the

NHRP Registration Request is considered to be valid by the NHS

initiating the synchronization event.

Cli Addr T/L

Type & length of next hop NBMA address (see [1]).

Cli SAddr T/L

Type & length of next hop NBMA subaddress (see [1]).

Cli Proto Len

This field holds the length in octets of the Client Protocol

Address.

Preference

This field specifies the preference value for use of the next hop

NBMA information specified.

Client NBMA Address

This is the client's NBMA address.

Client NBMA SubAddress

This is the client's NBMA subaddress.

Client Protocol Address

This is the client's internetworking layer address.

4. Values for SCSP Protocol Independent Part

The following sections give values for fields of the SCSP Protocol

Independent Part of the various SCSP messages.

4.1 Values for the SCSP "Mandatory Common Part"

Protocol ID = 0x0002

Sender ID Len = 0x04

Recvr ID Len = 0x04

See Section B.2.0.1 of [2] for a detailed description of these

fields.

4.2 Values for the SCSP "CSAS Record"

Cache Key Len = 0x04

Orig ID Len = 0x04

See Section B.2.0.2 of [2] for a detailed description of these

fields.

5. Security Considerations

Relevant security considerations are documented in [1] and [2].

References

[1] Luciani, J., Katz, D., Piscitello, D., Cole, B., and N.

Doraswamy, "NMBA Next Hop Resolution Protocol (NHRP)", RFC2332,

April 1998.

[2] Luciani, J., Armitage, G., Halpern, J., and N. Doraswamy, "Server

Cache Synchronization Protocol (SCSP)", RFC2334, April 1998.

[3] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC1700,

October 1994.

[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement

Levels", BCP 14, RFC2119, March 1997.

Acknowledgments

I would like to thank (in no particular order) Maxine Burns of ISR

and Joel Halpern of Newbridge. I would also like to thank the

members of the ION working group of the IETF, whose review and

discussion of this document has been invaluable.

Author's Address

James V. Luciani

Bay Networks, Inc.

3 Federal Street, BL3-03

Billerica, MA 01821

Phone: +1-978-916-4734

EMail: luciani@baynetworks.com

Full Copyright Statement

Copyright (C) The Internet Society (1998). All Rights Reserved.

This document and translations of it may be copied and furnished to

others, and derivative works that comment on or otherwise eXPlain it

or assist in its implementation may be prepared, copied, published

and distributed, in whole or in part, without restriction of any

kind, provided that the above copyright notice and this paragraph are

included on all such copies and derivative works. However, this

document itself may not be modified in any way, such as by removing

the copyright notice or references to the Internet Society or other

Internet organizations, except as needed for the purpose of

developing Internet standards in which case the procedures for

copyrights defined in the Internet Standards process must be

followed, or as required to translate it into languages other than

English.

The limited permissions granted above are perpetual and will not be

revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an

"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING

TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING

BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF

MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

 
 
 
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