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RFC2225 - Classical IP and ARP over ATM

王朝other·作者佚名  2008-05-31
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Network Working Group M. Laubach

Request for Comments: 2225 Com21, Inc.

Category: Standards Track J. Halpern

Obsoletes: 1626, 1577 Newbridge Networks, Inc.

April 1998

Classical IP and ARP over ATM

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. ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2. ACKNOWLEDGMENT . . . . . . . . . . . . . . . . . . . . . . . 2

3. CONVENTIONS . . . . . . . . . . . . . . . . . . . . . . . . . 3

4. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 3

5. IP SUBNETWORK CONFIGURATION . . . . . . . . . . . . . . . . . 6

5.1 Background . . . . . . . . . . . . . . . . . . . . . . . . 6

5.2 LIS Configuration Requirements . . . . . . . . . . . . . . 7

5.3 LIS Router Additional Configuration . . . . . . . . . . . . 8

6. IP PACKET FORMAT . . . . . . . . . . . . . . . . . . . . . . 8

7. DEFAULT VALUE FOR IP MTU OVER ATM AAL5 . . . . . . . . . . . 9

7.1 Permanent Virtual Circuits . . . . . . . . . . . . . . . . 9

7.2 Switched Virtual Circuits . . . . . . . . . . . . . . . . . 9

7.3 Path MTU Discovery Required . . . . . . . . . . . . . . . . 11

8. LIS ADDRESS RESOLUTION SERVICES . . . . . . . . . . . . . . . 11

8.1 ATM-based ARP and InARP Equivalent Services . . . . . . . . 11

8.2 Permanent Virtual Connections . . . . . . . . . . . . . . . 12

8.3 Switched Virtual Connections . . . . . . . . . . . . . . . 12

8.4 ATMARP Single Server Operational Requirements . . . . . . . 13

8.5 ATMARP Client Operational Requirements . . . . . . . . . . 14

8.5.1 Client ATMARP Table Aging . . . . . . . . . . . . . . . . 16

8.5.2 Non-Normal VC Operations . . . . . . . . . . . . . . . . 17

8.5.3 Use of ATM ARP in Mobile-IP Scenarios . . . . . . . . . . 17

8.6 Address Resolution Server Selection . . . . . . . . . . . . 17

8.6.1 PVCs to ATMARP Servers . . . . . . . . . . . . . . . . . 18

8.7 ATMARP Packet Formats . . . . . . . . . . . . . . . . . . . 18

8.7.1 ATMARP/InATMARP Request and Reply Packet Formats . . . . 18

8.7.2 Receiving Unknown ATMARP packets . . . . . . . . . . . . 20

8.7.3 TL, ATM Number, and ATM Subaddress Encoding . . . . . . . 20

8.7.4 ATMARP_NAK Packet Format . . . . . . . . . . . . . . . . 21

8.7.5 Variable Length Requirements for ATMARP Packets . . . . . 21

8.8 ATMARP/InATMARP Packet Encapsulation . . . . . . . . . . . 22

9. IP BROADCAST ADDRESS . . . . . . . . . . . . . . . . . . . . 23

10. IP MULTICAST ADDRESS . . . . . . . . . . . . . . . . . . . . 23

11. SECURITY CONSIDERATIONS . . . . . . . . . . . . . . . . . . 23

12. MIB SPECIFICATION . . . . . . . . . . . . . . . . . . . . . 24

13. OPEN ISSUES . . . . . . . . . . . . . . . . . . . . . . . . 24

14. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . 24

15. AUTHORS' ADDRESSES . . . . . . . . . . . . . . . . . . . . . 26

APPENDIX A - Update Information . . . . . . . . . . . . . . . . 27

FULL COPYRIGHT STATEMENT . . . . . . . . . . . . . . . . . . . . 28

1. ABSTRACT

This memo defines an initial application of classical IP and ARP in

an Asynchronous Transfer Mode (ATM) network environment configured as

a Logical IP Subnetwork (LIS) as described in Section 5. This memo

does not preclude the subsequent development of ATM technology into

areas other than a LIS; specifically, as single ATM networks grow to

replace many Ethernet local LAN segments and as these networks become

globally connected, the application of IP and ARP will be treated

differently. This memo considers only the application of ATM as a

direct replacement for the "wires" and local LAN segments connecting

IP end-stations ("members") and routers operating in the "classical"

LAN-based paradigm. Issues raised by MAC level bridging and LAN

emulation are beyond the scope of this paper.

This memo introduces general ATM technology and nomenclature.

Readers are encouraged to review the ATM Forum and ITU-TS (formerly

CCITT) references for more detailed information about ATM

implementation agreements and standards.

2. ACKNOWLEDGMENT

The authors would like to thank the efforts of the IP over ATM

Working Group of the IETF. Without their substantial, and sometimes

contentious support, of the Classical IP over ATM model, this updated

memo would not have been possible. Section 7, on Default MTU, has

been incorporated directly from Ran Atkinson's RFC1626, with his

permission. Thanks to Andy Malis for an early review and comments

for rolc and ion related issues.

3. CONVENTIONS

The key Words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",

"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this

document are to be interpreted as described in RFC2119 [20].

4. INTRODUCTION

The goal of this specification is to allow compatible and

interoperable implementations for transmitting IP datagrams and ATM

Address Resolution Protocol (ATMARP) requests and replies over ATM

Adaptation Layer 5 (AAL5)[2,6].

This memo specifies the stable foundation baseline operational model

which will always be available in IP and ARP over ATM

implementations. Subsequent memos will build upon and refine this

model. However, in the absence or failure of those extensions,

operations will default to the specifications contained in this memo.

Consequently, this memo will not reference these other extensions.

This memo defines only the operation of IP and address resolution

over ATM, and is not meant to describe the operation of ATM networks.

Any reference to virtual connections, permanent virtual connections,

or switched virtual connections applies only to virtual channel

connections used to support IP and address resolution over ATM, and

thus are assumed to be using AAL5. This memo places no restrictions

or requirements on virtual connections used for other purposes.

Initial deployment of ATM provides a LAN segment replacement for:

1) Local area networks (e.g., Ethernets, Token Rings and FDDI).

2) Local-area backbones between existing (non-ATM) LANs.

3) Dedicated circuits or frame relay PVCs between IP routers.

NOTE: In 1), local IP routers with one or more ATM interfaces will be

able to connect islands of ATM networks. In 3), public or private

ATM Wide Area networks will be used to connect IP routers, which in

turn may or may not connect to local ATM networks. ATM WANs and LANs

may be interconnected.

Private ATM networks (local or wide area) will use the private ATM

address structure specified in the ATM Forum UNI 3.1 specification

[9] or as in the ATM Forum UNI 4.0 specification [19]. This

structure is modeled after the format of an OSI Network Service

Access Point Address (NSAPA). A private ATM address uniquely

identifies an ATM endpoint.

Public networks will use either the address structure specified in

ITU-TS recommendation E.164 or the private network ATM address

structure. An E.164 address uniquely identifies an interface to a

public network.

The characteristics and features of ATM networks are different than

those found in LANs:

o ATM provides a Virtual Connection (VC) switched environment. VC

setup may be done on either a Permanent Virtual Connection (PVC)

or dynamic Switched Virtual Connection (SVC) basis. SVC call

management signalling is performed via implementations of the UNI

3.1 protocol [7,9].

o Data to be passed by a VC is segmented into 53 octet quantities

called cells (5 octets of ATM header and 48 octets of data).

o The function of mapping user Protocol Data Units (PDUs) into the

information field of the ATM cell and vice versa is performed in

the ATM Adaptation Layer (AAL). When a VC is created a specific

AAL type is associated with the VC. There are four different AAL

types, which are referred to individually as "AAL1", "AAL2",

"AAL3/4", and "AAL5". (NOTE: this memo concerns itself with the

mapping of IP and ATMARP over AAL5 only. The other AAL types are

mentioned for introductory purposes only.) The AAL type is known

by the VC end points via the call setup mechanism and is not

carried in the ATM cell header. For PVCs the AAL type is

administratively configured at the end points when the Connection

(circuit) is set up. For SVCs, the AAL type is communicated

along the VC path via UNI 3.1 as part of call setup establishment

and the end points use the signaled information for

configuration. ATM switches generally do not care about the AAL

type of VCs. The AAL5 format specifies a packet format with a

maximum size of (64K - 1) octets of user data. Cells for an AAL5

PDU are transmitted first to last, the last cell indicating the

end of the PDU. ATM standards guarantee that on a given VC, cell

ordering is preserved end-to-end. NOTE: AAL5 provides a non-

assured data transfer service - it is up to higher-level

protocols to provide retransmission.

o ATM Forum signaling defines point-to-point and point-to-

point Connection setup [9, 19.] Multipoint-to-multipoint not yet

specified by ITU-TS or ATM Forum.

An ATM Forum ATM address is either encoded as an NSAP form ATM

EndSystem Address (AESA) or is an E.164 Public-UNI address [9,

19]. In some cases, both an AESA and an E.164 Public UNI address

are needed by an ATMARP client to reach another host or router.

Since the use of AESAs and E.164 public UNI addresses by ATMARP

are analogous to the use of Ethernet addresses, the notion of

"hardware address" is extended to encompass ATM addresses in the

context of ATMARP, even though ATM addresses need not have

hardware significance. ATM Forum NSAP format addresses (AESA)

use the same basic format as U.S. GOSIP OSI NSAPAs [11]. NOTE:

ATM Forum addresses should not be construed as being U.S. GOSIP

NSAPAs. They are not, the administration is different, which

fields get filled out are different, etc. However, in this

document, these will be referred to as NSAPAs.

This memo describes the initial deployment of ATM within "classical"

IP networks as a direct replacement for local area networks

(Ethernets) and for IP links which interconnect routers, either

within or between administrative domains. The "classical" model here

refers to the treatment of the ATM host adapter as a networking

interface to the IP protocol stack operating in a LAN-based paradigm.

Characteristics of the classical model are:

o The same maximum transmission unit (MTU) size is the default for

all VCs in a LIS. However, on a VC-by-VC point-to-point basis,

the MTU size may be negotiated during connection setup using Path

MTU Discovery to better suit the needs of the cooperating pair of

IP members or the attributes of the communications path. (Refer

to Section 7.3)

o Default LLC/SNAP encapsulation of IP packets.

o End-to-end IP routing architecture stays the same.

o IP addresses are resolved to ATM addresses by use of an ATMARP

service within the LIS - ATMARPs stay within the LIS. From a

client's perspective, the ATMARP architecture stays faithful to

the basic ARP model presented in [3].

o One IP subnet is used for many hosts and routers. Each VC

directly connects two IP members within the same LIS.

Future memos will describe the operation of IP over ATM when ATM

networks become globally deployed and interconnected.

The deployment of ATM into the Internet community is just beginning

and will take many years to complete. During the early part of this

period, we eXPect deployment to follow traditional IP subnet

boundaries for the following reasons:

o Administrators and managers of IP subnetworks will tend to

initially follow the same models as they currently have deployed.

The mindset of the community will change slowly over time as ATM

increases its coverage and builds its credibility.

o Policy administration practices rely on the security, access,

routing, and filtering capability of IP Internet gateways: i.e.,

firewalls. ATM will not be allowed to "back-door" around these

mechanisms until ATM provides better management capability than

the existing services and practices.

o Standards for global IP over ATM will take some time to complete

and deploy.

This memo details the treatment of the classical model of IP and

ATMARP over ATM. This memo does not preclude the subsequent

treatment of ATM networks within the IP framework as ATM becomes

globally deployed and interconnected; this will be the subject of

future documents. This memo does not address issues related to

transparent data link layer interoperability.

5. IP SUBNETWORK CONFIGURATION

5.1 Background

In the LIS scenario, each separate administrative entity configures

its hosts and routers within a LIS. Each LIS operates and

communicates independently of other LISs on the same ATM network.

In the classical model, hosts communicate directly via ATM to other

hosts within the same LIS using the ATMARP service as the mechanism

for resolving target IP addresses to target ATM endpoint addresses.

The ATMARP service has LIS scope only and serves all hosts in the

LIS. Communication to hosts located outside of the local LIS is

provided via an IP router. This router is an ATM endpoint attached

to the ATM network that is configured as a member of one or more

LISs. This configuration MAY result in a number of disjoint LISs

operating over the same ATM network. Using this model hosts of

differing IP subnets MUST communicate via an intermediate IP router

even though it may be possible to open a direct VC between the two IP

members over the ATM network.

By default, the ATMARP service and the classical LIS routing model

MUST be available to any IP member client in the LIS.

5.2 LIS Configuration Requirements

The requirements for IP members (hosts, routers) operating in an ATM

LIS configuration are:

o All members of the LIS have the same IP network/subnet number and

address mask [8].

o All members within a LIS are directly connected to the ATM

network.

o All members of a LIS MUST have a mechanism for resolving IP

addresses to ATM addresses via ATMARP (based on [3]) and vice

versa via InATMARP (based on [12]) when using SVCs. Refer to

Section 8 "LIS ADDRESS RESOLUTION SERVICES" in this memo.

o All members of a LIS MUST have a mechanism for resolving VCs to

IP addresses via InATMARP (based on [12]) when using PVCs. Refer

to Section 8 "LIS ADDRESS RESOLUTION SERVICES" in this memo.

o All members within a LIS MUST be able to communicate via ATM with

all other members in the same LIS; i.e., the Virtual Connection

topology underlying the intercommunication among the members is

fully meshed.

The following list identifies the set of ATM specific parameters that

MUST be implemented in each IP station connected to the ATM network:

o ATM Hardware Address (atm$ha). The ATM address of the individual

IP station.

o ATMARP Request Address list (atm$arp-req-list): atm$arp-req-list

is a list containing one or more ATM addresses of individual

ATMARP servers located within the LIS. In an SVC environment,

ATMARP servers are used to resolve target IP addresses to target

ATM address via an ATMARP request and reply protocol. ATMARP

servers MUST have authoritative responsibility for resolving

ATMARP requests of all IP members using SVCs located within the

LIS.

A LIS MUST have a single ATMARP service entry configured and

available to all members of the LIS who use SVCs.

In the case where there is only a single ATMARP server within the

LIS, then all ATMARP clients MUST be configured identically to have

only one non-null entry in atm$arp-req-list configured with the same

address of the single ATMARP service.

If the IP member is operating with PVCs only, then atm$arp-req-list

MUST be configured with all null entries and the client MUST not make

queries to either address resolution service.

Within the restrictions mentioned above and in Section 8, local

administration MUST decide which server address(es) are appropriate

for atm$arp-req-list.

By default, atm$arp-req-list MUST be configured using the MIB [18].

Manual configuration of the addresses and address lists presented in

this section is implementation dependent and beyond the scope of this

document; i.e., this memo does not require any specific configuration

method. This memo does require that these addresses MUST be

configured completely on the client, as appropriate for the LIS,

prior to use by any service or operation detailed in this memo.

5.3 LIS Router Additional Configuration

It is RECOMMENDED that routers providing LIS functionality over the

ATM network also support the ability to interconnect multiple LISs.

Routers that wish to provide interconnection of differing LISs MUST

be able to support multiple sets of these parameters (one set for

each connected LIS) and be able to associate each set of parameters

to a specific IP network/ subnet number. In addition, it is

RECOMMENDED that a router be able to provide this multiple LIS

support with a single physical ATM interface that may have one or

more individual ATM endpoint addresses. NOTE: this does not

necessarily mean different End System Identifiers (ESIs) when NSAPAs

are used. The last octet of an NSAPA is the NSAPA Selector (SEL)

field which can be used to differentiate up to 256 different LISs for

the same ESI. (Refer to Section 5.1.3.1, "Private Networks" in [9].)

6. IP PACKET FORMAT

Implementations MUST support IEEE 802.2 LLC/SNAP encapsulation as

described in [2]. LLC/SNAP encapsulation is the default packet

format for IP datagrams.

This memo recognizes that other encapsulation methods may be used

however, in the absence of other knowledge or agreement, LLC/SNAP

encapsulation is the default.

This memo recognizes that end-to-end signaling within ATM may allow

negotiation of encapsulation method on a per-VC basis.

7. DEFAULT VALUE FOR IP MTU OVER ATM AAL5

Protocols in wide use throughout the Internet, such as the Network

File System (NFS), currently use large frame sizes (e.g., 8 KB).

Empirical evidence with various applications over the Transmission

Control Protocol (TCP) indicates that larger Maximum Transmission

Unit (MTU) sizes for the Internet Protocol (IP) tend to give better

performance. Fragmentation of IP datagrams is known to be highly

undesirable [16]. It is desirable to reduce fragmentation in the

network and thereby enhance performance by having the IP Maximum

Transmission Unit (MTU) for AAL5 be reasonably large. NFS defaults

to an 8192 byte frame size. Allowing for RPC/XDR, UDP, IP, and LLC

headers, NFS would prefer a default MTU of at least 8300 octets.

Routers can sometimes perform better with larger packet sizes because

most of the performance costs in routers relate to "packets handled"

rather than "bytes transferred". So, there are a number of good

reasons to have a reasonably large default MTU value for IP over ATM

AAL5.

RFC1209 specifies the IP MTU over SMDS to be 9180 octets, which is

larger than 8300 octets but still in the same range [1]. There is no

good reason for the default MTU of IP over ATM AAL5 to be different

from IP over SMDS, given that they will be the same magnitude.

Having the two be the same size will be helpful in interoperability

and will also help reduce incidence of IP fragmentation.

Therefore, the default IP MTU for use with ATM AAL5 shall be 9180

octets. All implementations compliant and conformant with this

specification shall support at least the default IP MTU value for use

over ATM AAL5.

7.1 Permanent Virtual Circuits

Implementations which only support Permanent Virtual Circuits (PVCs)

will (by definition) not implement any ATM signalling protocol. Such

implementations shall use the default IP MTU value of 9180 octets

unless both parties have agreed in advance to use some other IP MTU

value via some mechanism not specified here.

7.2 Switched Virtual Circuits

Implementations that support Switched Virtual Circuits (SVCs) MUST

attempt to negotiate the AAL CPCS-SDU size using the ATM signalling

protocol. The industry standard ATM signalling protocol uses two

different parts of the Information Element named "AAL Parameters" to

exchange information on the MTU over the ATM circuit being setup [9].

The Forward Maximum CPCS-SDU Size field contains the value over the

path from the calling party to the called party. The Backwards

Maximum CPCS-SDU Size Identifier field contains the value over the

path from the called party to the calling party. The ATM Forum

specifies the valid values of this identifier as 1 to 65535

inclusive. Note that the ATM Forum's User-to-Network-Interface (UNI)

signalling permits the MTU in one direction to be different from the

MTU in the opposite direction, so the Forward Maximum CPCS-SDU Size

Identifier might have a different value from the Backwards Maximum

CPCS-SDU Size Identifier on the same connection.

If the calling party wishes to use the default MTU it shall still

include the "AAL Parameters" information element with the default

values for the Maximum CPCS-SDU Size as part of the SETUP message of

the ATM signalling protocol [9]. If the calling party desires to use

a different value than the default, it shall include the "AAL

Parameters" information element with the desired value for the

Maximum CPCS-SDU Size as part of the SETUP message of the ATM

Signalling Protocol. The called party will respond using the same

information elements and identifiers in its CONNECT message response

[9].

If the called party receives a SETUP message containing the "Maximum

CPCS-SDU Size" in the AAL Parameters information element, it shall

handle the Forward and Backward Maximum CPCS-SDU Size Identifier as

follows:

a) If it is able to accept the ATM MTU values proposed by the SETUP

message, it shall include an AAL Parameters information element

in its response. The Forward and Backwards Maximum CPCS-SDU Size

fields shall be present and their values shall be equal to the

corresponding values in the SETUP message.

b) If it wishes a smaller ATM MTU size than that proposed, then it

shall set the values of the Maximum CPCS-SDU Size in the AAL

Parameters information elements equal to the desired value in the

CONNECT message responding to the original SETUP message.

c) If the calling endpoint receives a CONNECT message that does not

contain the AAL Parameters Information Element, but the

corresponding SETUP message did contain the AAL Parameters

Information element (including the forward and backward CPCS-SDU

Size fields), it shall clear the call with cause "AAL Parameters

cannot be supported".

d) If either endpoint receives a STATUS message with cause

"Information Element Non-existent or Not Implemented" or cause

"Access Information Discarded", and with a diagnostic field

indicating the AAL Parameters Information Element identifier, it

shall clear the call with cause "AAL Parameters cannot be

supported."

e) If either endpoint receives CPCS-SDUs in excess of the negotiated

MTU size, it may use IP fragmentation or may clear the call with

cause "AAL Parameters cannot be supported". In this case, an

error has occurred either due to a fault in an end system or in

the ATM network. The error should be noted by ATM network

management for human examination and intervention.

If the called endpoint incorrectly includes the Forward and Backward

Maximum CPCS-SDU Size fields in the CONNECT messages (e.g., because

the original SETUP message did not include these fields) or it sets

these fields to an invalid value, then the calling party shall clear

the call with cause "Invalid Information Element Contents".

7.3 Path MTU Discovery Required

The Path MTU Discovery mechanism is Internet Standard RFC1191 [17]

and is an important mechanism for reducing IP fragmentation in the

Internet. This mechanism is particularly important because new

subnet ATM uses a default MTU sizes significantly different from

older subnet technologies such as Ethernet and FDDI.

In order to ensure good performance throughout the Internet and also

to permit IP to take full advantage of the potentially larger IP

datagram sizes supported by ATM, all router implementations that

comply or conform with this specification must also implement the IP

Path MTU Discovery mechanism as defined in RFC1191 and clarified by

RFC1435 [14]. Host implementations should implement the IP Path MTU

Discovery mechanism as defined in RFC1191.

8. LIS ADDRESS RESOLUTION SERVICES

8.1 ATM-based ARP and InARP Equivalent Services

Address resolution within an ATM LIS SHALL make use of the ATM

Address Resolution Protocol (ATMARP) (based on [3]) and the Inverse

ATM Address Resolution Protocol (InATMARP) (based on [12]) and as

defined in this memo. ATMARP is the same protocol as the ARP

protocol presented in [3] with extensions needed to support address

resolution in a unicast server ATM environment. InATMARP is the same

protocol as the original InARP protocol presented in [12] but applied

to ATM networks. All IP stations MUST support these protocols as

updated and extended in this memo. Use of these protocols differs

depending on whether PVCs or SVCs are used.

8.2 Permanent Virtual Connections

An IP station MUST have a mechanism (e.g., manual configuration) for

determining what PVCs it has, and in particular which PVCs are being

used with LLC/SNAP encapsulation. The details of the mechanism are

beyond the scope of this memo.

All IP members supporting PVCs are required to use the Inverse ATM

Address Resolution Protocol (InATMARP) (refer to [12]) on those VCs

using LLC/SNAP encapsulation. In a strict PVC environment, the

receiver SHALL infer the relevant VC from the VC on which the

InATMARP_Request or response InATMARP_Reply was received. When the

ATM source and/or target address is unknown, the corresponding ATM

address length in the InATMARP packet MUST be set to zero (0)

indicating a null length, and no storage be allocated in the InATMARP

packet, otherwise the appropriate address field should be filled in

and the corresponding length set appropriately. InATMARP packet

format details are presented later in this memo.

Directly from [12]: "When the requesting station receives the

In[ATM]ARP_Reply, it may complete the [ATM]ARP table entry and use

the provided address information. NOTE: as with [ATM]ARP,

information learned via In[ATM]ARP may be aged or invalidated under

certain circumstances." IP stations supporting PVCs MUST re-validate

ATMARP table entries as part of the table aging process. See the

Section 8.5.1 "Client ATMARP Table Aging".

If a client has more than one IP address within the LIS and if using

PVCs, when an InATMARP_Request is received an InATMARP_Reply MUST be

generated for each such address.

8.3 Switched Virtual Connections

SVCs require support from address resolution services for resolving

target IP addresses to target ATM endpoint addresses. All members in

the LIS MUST use the same service. This service MUST have

authoritative responsibility for resolving the ATMARP requests of all

IP members within the LIS.

ATMARP servers do not actively establish connections. They depend on

the clients in the LIS to initiate connections for the ATMARP

registration procedure and for transmitting ATMARP requests. An

individual client connects to the ATMARP server using a point-to-

point LLC/SNAP VC. The client sends normal ATMARP request packets to

the server. The ATMARP server examines each ATMARP_Request packet

for

the source protocol and source hardware address information of the

sending client and uses this information to build its ATMARP table

cache. This information is used to generate replies to any ATMARP

requests it receives.

InATMARP_Request packets MUST specify valid address information for

ATM source number, ATM target number, and source protocol address;

i.e., these fields MUST be non-null in InATMARP_Request packets.

This memo defines the address resolution service in the LIS and

constrains it to consist of a single ATMARP server. Client-server

interaction is defined by using a single server approach as a

reference model.

This memo recognizes the future development of standards and

implementations of multiple-ATMARP-server models that will extend the

operations as defined in this memo to provide a highly reliable

address resolution service.

8.4 ATMARP Single Server Operational Requirements

A single ATMARP server accepts ATM calls/connections from other ATM

end points. After receiving any ATMARP_Request, the server will

examine the source and target address information in the packet and

make note of the VC on which the ATMARP_Request arrived. It will use

this information as necessary to build and update its ATMARP table

entries.

For each ATMARP_Request, then:

1. If the source IP protocol address is the same as the target IP

protocol address and a table entry exists for that IP address and

if the source ATM hardware address does not match the table entry

ATM address and there is an open VC associated with that table

entry that is not the same as the VC associated with the

ATMARP_Request, the server MUST return the table entry

information in the ATMARP_Reply, and MUST raise a "duplicate IP

address detected" condition to the server's management. The

table entry is not updated.

2. Otherwise, if the source IP protocol address is the same as the

target IP protocol address, and either there is no table entry

for that IP address, or a table entry exists for that IP address

and there is no open VC associated with that table entry, or if

the VC associated with that entry is the same as the VC for the

ATMARP_Request, the server MUST either create a new entry or

update the old entry as appropriate and return that table entry

information in the ATMARP Reply.

3. Otherwise, when the source IP protocol address does not match the

target IP protocol address, the ATMARP server will generate the

corresponding ATMARP_Reply if it has an entry for the target

information in its ATMARP table. Otherwise, it will generate a

negative ATMARP reply (ATMARP_NAK).

4. Additionally, when the source IP protocol address does not match

the target IP protocol address and when the server receives an

ATMARP_Request over a VC, where the source IP and ATM address do

not have a corresponding table entry, the ATMARP server MUST

create a new table entry for the source information.

Explanation: this allows old RFC1577 clients to register with

this ATMARP service by just issuing requests to it.

5. Additionally, when the source IP protocol address does not match

the target IP protocol address and where the source IP and ATM

addresses match the association already in the ATMARP table and

the ATM address matches that associated with the VC, the server

MUST update the table timeout on the source ATMARP table entry

but only if it has been more than 10 minutes since the last

update. Explanation: if the client is sending ATMARP requests to

the server over the same VC that it used to register its ATMARP

entry, the server should examine the ATMARP request and note that

the client is still "alive" by updating the timeout on the

client's ATMARP table entry.

6. Additionally, when the source IP protocol address does not match

the target IP protocol address and where the source IP and ATM

addresses do not match the association already in the ATMARP

table, the server MUST NOT update the ATMARP table entry.

An ATMARP server MUST have knowledge of any open VCs it has and their

association with an ATMARP table entry, and in particular, which VCs

support LLC/SNAP encapsulation. In normal operation, active ATMARP

clients will revalidate their entries prior to the server aging

process taking effect.

Server ATMARP table entries are valid for 20 minutes. If an entry

ages beyond 20 minutes without being updated (refreshed) by the

client, that entry is deleted from the table regardless of the state

of any VCs that may be associated with that entry.

8.5 ATMARP Client Operational Requirements

The ATMARP client is responsible for contacting the ATMARP service to

both initially register and subsequently refresh its own ATMARP

information.

The client is also responsible for using the ATMARP service to gain

and revalidate ATMARP information about other IP members in the LIS

(server selection overview is discussed in Section 8.6). As noted in

Section 5.2, ATMARP clients MUST be configured with the ATM address

of the appropriate server prior to client ATMARP operation.

IP clients MUST register their ATM endpoint address with their ATMARP

server using the ATM address structure appropriate for their ATM

network connection: i.e., LISs implemented over ATM LANs following

ATM Forum UNI 3.1 should register using Structure 1; LISs implemented

over an E.164 "public" ATM network should register using Structure 2.

A LIS implemented over a combination of ATM LANs and public ATM

networks may need to register using Structure 3. Implementations

based on this memo MUST support all three ATM address structures.

See Section 8.7.1 for more details regarding the ATMARP Request

packet format.

To handle the case when a client has more than one IP address within

a LIS, when using an ATMARP server, the client MUST register each

such address.

For initial registration and subsequent refreshing of its own

information with the ATMARP service, clients MUST:

1. Establish an LLC/SNAP VC connection to a server in the ATMARP

service for the purposes of transmitting and receiving ATMARP

packets.

NOTE: in the case of refreshing its own information with the

ATMARP service, a client MAY reuse an existing established

connection to the ATMARP service provided that the connection was

previously used either to initially register its information with

the ATMARP service or to refresh its information with the ATMARP

service.

2. After establishing a successful connection to the ATMARP service,

the client MUST transmit an ATMARP_Request packet, requesting a

target ATM address for its own IP address as the target IP

protocol address. The client checks the ATMARP_Reply and if the

source hardware and protocol addresses match the respective

target hardware and protocol addresses, the client is registered

with the ATMARP service. If the addresses do not match, the

client MAY take action, raise alarms, etc.; however, these

actions are beyond the scope of this memo. In the case of a

client having more than one IP address in the list, this step

MUST be repeated for each IP address.

3. Clients MUST respond to ATMARP_Request and InATMARP_Request

packets received on any VC appropriately. (Refer to Section 7,

"Protocol Operation" in RFC1293 [12].)

NOTE: for reasons of robustness, clients MUST respond to

ATMARP_Requests.

4. Generate and transmit address resolution request packets to the

address resolution service. Respond to address resolution reply

packets appropriately to build/refresh its own client ATMARP

table entries.

5. Generate and transmit InATMARP_Request packets as needed and

process InATMARP_Reply packets appropriately. InATMARP_Reply

packets should be used to build/refresh its own client ATMARP

table entries. (Refer to Section 7, "Protocol Operation" in

[12].) If a client has more than one IP address within the LIS

when an InATMARP_Request is received an InATMARP_Reply MUST be

generated for each such address.

The client MUST refresh its ATMARP information with the server at

least once every 15 minutes. This is done by repeating steps 1 and

2.

An ATMARP client MUST have knowledge of any open VCs it has

(permanent or switched), their association with an ATMARP table

entry, and in particular, which VCs support LLC/SNAP encapsulation.

8.5.1 Client ATMARP Table Aging

Client ATMARP table entries are valid for a maximum time of 15

minutes.

When an ATMARP table entry ages, an ATMARP client MUST invalidate the

table entry. If there is no open VC server associated with the

invalidated entry, that entry is deleted. In the case of an

invalidated entry and an open VC, the client MUST revalidate the

entry prior to transmitting any non address resolution traffic on

that VC; this requirement applies to both PVCs and SVCs. NOTE: the

client is permitted to revalidate an ATMARP table entry before it

ages, thus restarting the aging time when the table entry is

successfully revalidated. The client MAY continue to use the open

VC, as long as the table entry has not aged, while revalidation is in

progress.

In the case of an open PVC, the client revalidates the entry by

transmitting an InATMARP_Request and updating the entry on receipt of

an InATMARP_Reply.

In the case of an open SVC, the client revalidates the entry by

querying the address resolution service. If a valid reply is

received (e.g., ATMARP_Reply), the entry is updated. If the address

resolution service cannot resolve the entry (i.e., "host not found"),

the SVC should be closed and the associated table entry removed. If

the address resolution service is not available (i.e., "server

failure") and if the SVC is LLC/SNAP encapsulated, the client MUST

attempt to revalidate the entry by transmitting an InATMARP_Request

on that VC and updating the entry on receipt of an InATMARP_Reply.

If the InATMARP_Request attempt fails to return an InATMARP_Reply,

the SVC should be closed and the associated table entry removed.

If a VC with an associated invalidated ATMARP table entry is closed,

that table entry is removed.

8.5.2 Non-Normal VC Operations

The specific details on client procedures for detecting non-normal VC

connection establishment or closures, or failed communications on an

established VC are beyond the scope of this memo. It is REQUIRED

however, that the client MUST remove the associated ATMARP entry for

a VC that fails to operate properly, as defined by the client, when

the client closes that VC, when it releases its resources for a VC,

or prior to any attempt to reopen that VC. This behavior

specifically REQUIRES that the client MUST refresh its ATMARP table

information prior to any attempt to re-establish communication to an

IP member after a non-normal communications problem has previously

occurred on a VC to that IP member.

8.5.3 Use of ATMARP In Mobile-IP Scenarios

When an ATM LIS is used as the home network in a mobile-IP scenario,

it is RECOMMENDED that the home agent NOT maintain long term

connections with the ATMARP service. The absence of this VC will

permit a mobile node's registration, upon its return to the home

network, to immediately preempt the home agent's previous gratuitous

registration.

8.6 Address Resolution Server Selection

If the client supports PVCs only, the ATMARP server list is empty and

the client MUST not generate any address resolution requests other

than the InATMARP requests on a PVC needed to validate that PVC.

If the client supports SVCs, then the client MUST have a non-NULL

atm$arp-req-list pointing to the ATMARP server(s) which provides

ATMARP service for the LIS.

The client MUST register with a server from atm$arp-req-list.

The client SHALL attempt to communicate with any of the servers until

a successful registration is accomplished. The order in which client

selects servers to attempt registration, is a local matter, as are

the number of retries and timeouts for such attempts.

8.6.1 PVCs to ATMARP Servers

In a mixed PVC and SVC LIS environment, an ATMARP client MAY have a

PVC to an ATMARP server. In this case, this PVC is used for ATMARP

requests and responses as if it were an established SVC. NOTE: if

this PVC is to be used for IP traffic, then the ATMARP server MUST be

prepared to accept and respond appropriately to InATMARP traffic.

8.7 ATMARP Packet Formats

Internet addresses are assigned independently of ATM addresses. Each

host implementation MUST know its own IP and ATM address(es) and MUST

respond to address resolution requests appropriately. IP members

MUST also use ATMARP and InATMARP to resolve IP addresses to ATM

addresses when needed.

NOTE: the ATMARP packet format presented in this memo is general in

nature in that the ATM number and ATM subaddress fields SHOULD map

directly to the corresponding UNI 3.1 fields used for ATM

call/connection setup signalling messages. The IP over ATM Working

Group expects ATM Forum NSAPA numbers (Structure 1) to predominate

over E.164 numbers (Structure 2) as ATM endpoint identifiers within

ATM LANs. The ATM Forum's VC Routing specification is not complete

at this time and therefore its impact on the operational use of ATM

Address Structure 3 is undefined. The ATM Forum will be defining

this relationship in the future. It is for this reason that IP

members need to support all three ATM address structures.

8.7.1 ATMARP/InATMARP Request and Reply Packet Formats

The ATMARP and InATMARP request and reply protocols use the same

hardware type (ar$hrd), protocol type (ar$pro), and operation code

(ar$op) data formats as the ARP and InARP protocols [3,12]. The

location of these three fields within the ATMARP packet are in the

same byte position as those in ARP and InARP packets. A unique

hardware type value has been assigned for ATMARP. In addition,

ATMARP makes use of an additional operation code for ARP_NAK. The

remainder of the ATMARP/InATMARP packet format is different than the

ARP/InARP packet format.

The ATMARP and InATMARP protocols have several fields that have the

following format and values:

Data:

ar$hrd 16 bits Hardware type

ar$pro 16 bits Protocol type

ar$shtl 8 bits Type & length (TL) of source ATM number (q)

ar$sstl 8 bits Type & length (TL) of source ATM subaddress (r)

ar$op 16 bits Operation code (request, reply, or NAK)

ar$spln 8 bits Length of source protocol address (s)

ar$thtl 8 bits Type & length (TL) of target ATM number (x)

ar$tstl 8 bits Type & length (TL) of target ATM subaddress (y)

ar$tpln 8 bits Length of target protocol address (z)

ar$sha qoctets of source ATM number

ar$ssa roctets of source ATM subaddress

ar$spa soctets of source protocol address

ar$tha xoctets of target ATM number

ar$tsa yoctets of target ATM subaddress

ar$tpa zoctets of target protocol address

Where:

ar$hrd - assigned to ATM Forum address family and is

19 decimal (0x0013) [4].

ar$pro - see Assigned Numbers for protocol type number for

the protocol using ATMARP. (IP is 0x0800).

ar$shtl - Type and length of source ATM number. See

Section 8.7.4 for TL encoding details.

ar$sstl - Type and length of source ATM subaddress. See

Section 8.7.4 for TL encoding details.

ar$op - The operation type value (decimal):

ATMARP_Request = ARP_REQUEST = 1

ATMARP_Reply = ARP_REPLY = 2

InATMARP_Request = InARP_REQUEST = 8

InATMARP_Reply = InARP_REPLY = 9

ATMARP_NAK = ARP_NAK = 10

ar$spln - length in octets of the source protocol address. Value

range is 0 or 4 (decimal). For IPv4 ar$spln is 4.

ar$thtl - Type and length of target ATM number. See

Section 8.7.4 for TL encoding details.

ar$tstl - Type and length of target ATM subaddress. See

Section 8.7.4 for TL encoding details.

ar$tpln - length in octets of the target protocol address. Value

range is 0 or 4 (decimal). For IPv4 ar$tpln is 4.

ar$sha - source ATM number (E.164 or ATM Forum NSAPA)

ar$ssa - source ATM subaddress (ATM Forum NSAPA)

ar$spa - source protocol address

ar$tha - target ATM number (E.164 or ATM Forum NSAPA)

ar$tsa - target ATM subaddress (ATM Forum NSAPA)

ar$tpa - target protocol address

8.7.2 Receiving Unknown ATMARP packets

If an ATMARP client receives an ATMARP message with an operation code

(ar$op) for which it is not coded to support, it MUST gracefully

discard the message and continue normal operation. An ATMARP client

is NOT REQUIRED to return any message to the sender of the

unsupported message.

8.7.3 TL, ATM Number, and ATM Subaddress Encoding

The encoding of the 8-bit TL (type and length) fields in ATMARP and

In_ATMARP packets is as follows:

MSB 8 7 6 5 4 3 2 1 LSB

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

0 1/0 Octet length of address

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

Where:

bit.8 (reserved) = 0 (for future use)

bit.7 (type) = 0 ATM Forum NSAPA format

= 1 E.164 format

bit.6-1 (length) = 6 bit unsigned octet length of address

(MSB = bit.6, LSB = bit.1) Value

range is from 0 to 20 (decimal).

ATM addresses, as defined by the ATM Forum UNI 3.1 signaling

specification [9], include a "Calling Party Number Information

Element" and a "Calling Party Subaddress Information Element". These

Information Elements (IEs) SHOULD map to ATMARP/InATMARP source ATM

number and source ATM subaddress respectively. Furthermore, ATM

Forum defines a "Called Party Number Information Element" and a

"Called Party Subaddress Information Element". These IEs map to

ATMARP/InATMARP target ATM number and target ATM subaddress,

respectively.

The ATM Forum defines three structures for the combined use of number

and subaddress [9]:

ATM Number ATM Subaddress

-------------- --------------

Structure 1 ATM Forum NSAPA null

Structure 2 E.164 null

Structure 3 E.164 ATM Forum NSAPA

ATMARP and InATMARP requests and replies for ATM address structures 1

and 2 MUST indicate a null or unknown ATM subaddress by setting the

appropriate subaddress length to zero; i.e., ar$sstl.length = 0 or

ar$tstl.length = 0, the corresponding type field (ar$sstl.type or

ar$tstl.type) MUST be ignored and the physical space for the ATM

subaddress buffer MUST not be allocated in the ATMARP packet. For

example, if ar$sstl.length=0, the storage for the source ATM

subaddress is not allocated and the first byte of the source protocol

address ar$spa follows immediately after the last byte of the source

hardware address ar$sha in the packet.

Null or unknown ATM addresses MUST be indicated by setting the

appropriate address length to zero; i.e., ar$shtl.length and

ar$thtl.length is zero and the corresponding type field (ar$sstl.type

or ar$tstl.type) MUST be ignored and the physical space for the ATM

address or ATM subaddress buffer MUST not be allocated in the ATMARP

packet.

8.7.4 ATMARP_NAK Packet Format

The ATMARP_NAK packet format is the same as the received

ATMARP_Request packet format with the operation code set to ARP_NAK,

i.e., the ATMARP_Request packet data is exactly copied (e.g., using

bcopy) for transmission with the ATMARP_Request operation code

changed to ARP_NAK value.

8.7.5 Variable Length Requirements for ATMARP Packets

ATMARP and InATMARP packets are variable in length.

A null or unknown source or target protocol address is indicated by

the corresponding length set to zero: e.g., when ar$spln or ar$tpln

is zero the physical space for the corresponding address structure

MUST not be allocated in the packet.

For backward compatibility with previous implementations, a null IPv4

protocol address may be received with length = 4 and an allocated

address in storage set to the value 0.0.0.0. Receiving stations MUST

be liberal in accepting this format of a null IPv4 address. However,

on transmitting an ATMARP or InATMARP packet, a null IPv4 address

MUST only be indicated by the length set to zero and MUST have no

storage allocated.

8.8 ATMARP/InATMARP Packet Encapsulation

ATMARP and InATMARP packets are to be encoded in AAL5 PDUs using

LLC/SNAP encapsulation. The format of the AAL5 CPCS-SDU payload

field for ATMARP/InATMARP PDUs is:

Payload Format for ATMARP/InATMARP PDUs:

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

LLC 0xAA-AA-03

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

OUI 0x00-00-00

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

EtherType 0x08-06

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

ATMARP/InATMARP Packet

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

The LLC value of 0xAA-AA-03 (3 octets) indicates the presence of a

SNAP header.

The OUI value of 0x00-00-00 (3 octets) indicates that the following

two-bytes is an EtherType.

The EtherType value of 0x08-06 (2 octets) indicates ARP [4].

The total size of the LLC/SNAP header is fixed at 8-octets. This

aligns the start of the ATMARP packet on a 64-bit boundary relative

to the start of the AAL5 CPCS-SDU.

The LLC/SNAP encapsulation for ATMARP/InATMARP presented here is

consistent with the treatment of multiprotocol encapsulation of IP

over ATM AAL5 as specified in [2] and in the format of ATMARP over

IEEE 802 networks as specified in [5].

Traditionally, address resolution requests are broadcast to all

directly connected IP members within a LIS. It is conceivable in the

future that larger scaled ATM networks may handle ATMARP requests to

destinations outside the originating LIS, perhaps even globally;

issues raised by ATMARPing outside the LIS or by a global ATMARP

mechanism are beyond the scope of this memo.

9. IP BROADCAST ADDRESS

ATM does not support broadcast addressing, therefore there are no

mappings available from IP broadcast addresses to ATM broadcast

services. Note: this lack of mapping does not restrict members from

transmitting or receiving IP datagrams specifying any of the four

standard IP broadcast address forms as described in [8]. Members,

upon receiving an IP broadcast or IP subnet broadcast for their LIS,

MUST process the packet as if addressed to that station.

This memo recognizes the future development of standards and

implementations that will extend the operations as defined in this

memo to provide an IP broadcast capability for use by the classical

client.

10. IP MULTICAST ADDRESS

ATM does not directly support IP multicast address services,

therefore there are no mappings available from IP multicast addresses

to ATM multicast services. Current IP multicast implementations

(i.e., MBONE and IP tunneling, see [10]) will continue to operate

over ATM based logical IP subnets if operated in the WAN

configuration.

This memo recognizes the future development of ATM multicast service

addressing by the ATM Forum. When available and widely implemented,

the roll-over from the current IP multicast architecture to this new

ATM architecture will be straightforward.

This memo recognizes the future development of standards and

implementations that will extend the operations as defined in this

memo to provide an IP multicast capability for use by the classical

client.

11. SECURITY CONSIDERATIONS

Not all of the security issues relating to IP over ATM are clearly

understood at this time, due to the fluid state of ATM

specifications, newness of the technology, and other factors.

It is believed that ATM and IP facilities for authenticated call

management, authenticated end-to-end communications, and data

encryption will be needed in globally connected ATM networks. Such

future security facilities and their use by IP networks are beyond

the scope of this memo.

There are known security issues relating to host impersonation via

the address resolution protocols used in the Internet [13]. No

special security mechanisms have been added to the address resolution

mechanism defined here for use with networks using IP over ATM.

12. MIB SPECIFICATION

Clients built to this specification MUST implement and provide a

Management Information Base (MIB) as defined in "Definitions of

Managed Objects for Classical IP and ARP Over ATM Using SMIv2" [18].

13. OPEN ISSUES

o Automatic configuration of client ATM addresses via DHCP [15] or

via ATM UNI 3.1 Interim Local Management Interface (ILMI)

services would be a useful extended service addition to this

document and should be addressed in a separate memo.

o ATMARP packets are not authenticated. This is a potentially

serious flaw in the overall system by allowing a mechanism by

which corrupt information may be introduced into the server

system.

14. REFERENCES

[1] Piscitello, D., and J. Lawrence, "The Transmission of IP

Datagrams over the SMDS Service", STD 52, RFC1209, March 1991.

[2] Heinanen, J., "Multiprotocol Encapsulation over ATM Adaptation

Layer 5", RFC1483, July 1993.

[3] Plummer, D., "An Ethernet Address Resolution Protocol - or -

Converting Network Protocol Addresses to 48.bit Ethernet

Address for Transmission on Ethernet Hardware", STD 37, RFC

826, November 1982.

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

July 1992.

[5] Postel, J., and J. Reynolds, "A Standard for the Transmission

of IP Datagrams over IEEE 802 Networks", STD 43, RFC1042,

February 1988.

[6] CCITT, "Draft Recommendation I.363", CCITT Study Group XVIII,

Geneva, 19-29 January 1993.

[7] CCITT, "Draft text for Q.93B", CCITT Study Group XI, 23 September

- 2 October 1992.

[8] Braden, R., "Requirements for Internet Hosts -- Communication

Layers", STD 3, RFC1122, October 1989.

[9] ATM Forum, "ATM User-Network Interface (UNI) Specification

Version 3.1.", ISBN 0-13-393828-X, Prentice-Hall, Inc., Upper

Saddle River, NJ, 07458, September, 1994.

[10] Deering, S., "Host Extensions for IP Multicasting", STD 5,

RFC1112, August 1989.

[11] Colella, R., Gardner, E., and R. Callon, "Guidelines for OSI

NSAP Allocation in the Internet", RFC1237, July 1991.

[12] Bradely, T., and C. Brown, "Inverse Address Resolution

Protocol", RFC1293, January 1992.

[13] Bellovin, Steven M., "Security Problems in the TCP/IP Protocol

Suite", ACM Computer Communications Review, Vol. 19, Issue 2,

pp. 32-48, 1989.

[14] Knowles, S., "IESG Advice from Experience with Path MTU

Discovery", RFC1435, March 1993.

[15] Droms, R., "Dynamic Host Configuration Protocol", RFC1541,

March 1997.

[16] Kent C., and J. Mogul, "Fragmentation Considered Harmful",

Proceedings of the ACM SIGCOMM '87 Workshop on Frontiers in

Computer Communications Technology, August 1987.

[17] Mogul, J., and S. Deering, "Path MTU Discovery", RFC1191,

November 1990.

[18] Green, M., Luciani, J., White, K., and T. Kuo, "Definitions of

Managed Objects for Classical IP and ARP over ATM Using

SMIv2", RFC2320, April 1998.

[19] ATM Forum, "ATM User-Network Interface (UNI) Specification

Version 4.0", ATM Forum specfication af-sig-0061.000,

FTP://ftp.atmforum.com/, July, 1996.

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

Levels", BCP 14, RFC2119, March 1997.

15. AUTHORS' ADDRESSES

Mark Laubach

Com21, Inc.

750 Tasman Drive

Milpitas, CA 95035

Phone: 408.953.9175

FAX: 408.953.9299

EMail: laubach@com21.com

Joel Halpern

Newbridge Networks, Inc.

593 Herndon Parkway

Herndon, VA 22070-5241

Phone: 703.736.5954

FAX: 703.736.5959

EMail: jhalpern@Newbridge.com

APPENDIX A - Update Information

This memo represents an update to RFC1577 and RFC1626. The

following changes are included in this memo:

o Pointer to Classical MIB I-D for setting of variables

o Single ATMARP server address to ATMARP server list, configurable

via the MIB.

o RFC1626 text replaces MTU section

o Client registration procedure from In_ATMARP to first

ATMARP_Request

o Clarification of variable length ATMARP packet format

o Clarification of ARP_NAK packet format

o Clarification of InATMARP packet format for null IPv4 addresses

o Clarification on ATMARP registration and use of InATMARP_Reply

for clients having more than one IP address in a LIS

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 implmentation may be prepared, copied, published

andand 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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