RFC2603 - ILMI-Based Server Discovery for NHRP

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　　Network Working Group M. Davison
Request for Comments: 2603 Cisco Systems
Category: Standards Track June 1999

ILMI-Based Server Discovery for NHRP

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 (1999). All Rights Reserved.

Abstract

This memo defines how ILMI-based Server Discovery, which provides a
method for ATM-attached hosts and routers to dynamically determine
the ATM addresses of servers, shall be used to locate NHRP servers.

1. Introduction

Presently, configuring a host or router to use NHRP [1] is cumbersome
and error-prone since it requires at least one ATM address to be
statically configured on each host or router in the network.
Further, it is impossible to implement a diskless host to use NHRP
since local configuration is required. ILMI-based Server Discovery,
hereafter referred to as "server discovery," provides a solution to
these problems.

A brief overview of the Integrated Local Management Interface (ILMI)
and the Service Registry MIB, as defined by the ATM Forum, are
provided in this memo. The reader should consult [2] for a complete
description of ILMI and this MIB, but the information contained here
is sufficient for an understanding of its use to support NHRP server
discovery.

2. Integrated Local Management Interface

The Integrated Local Management Interface (ILMI) [2] provides a
mechanism for ATM-attached devices, such as hosts, routers, and ATM
switches, to transfer management information. It is based on the
Simple Network Management Protocol (SNMP), Version 1, and supports

get, get-next, set and trap operations.

The ILMI specification designates the switch side of the ATM link as
the 'network side' and the host/router side of the ATM link as the '
user side.' The Service Registry MIB, which is outlined in Section 3,
is implmented on the network side and is queried from the user side.

3. ILMI 4.0 Service Registry MIB

Server discovery utilizes the Service Registry MIB defined by the ATM
Forum in ILMI Specification Version 4.0 [2]. To support the existing
framework for IP over ATM, ATM switches must support the Service
Registry MIB.

A row in the service registry table [2] is defined as:

AtmfSrvcRegEntry ::= SEQUENCE {
atmfSrvcRegPort INTEGER,
atmfSrvcRegServiceID OBJECT IDENTIFIER,
atmfSrvcRegATMAddress AtmAddress,
atmfSrvcRegAddressIndex INTEGER,
atmfSrvcRegParm1 OCTET STRING
}

The definition of each field in this structure is:

atmfSrvcRegPort - The ATM port number for which this entry
contains management information. The value of zero may be used
to indicate the ATM interface over which a management request
was received.

atmfSrvcRegServiceID - This is the service identifier that
uniquely identifies the type of service at the address
provided in the table. (See Section 3.2 for NHRP OID.)

atmfSrvcRegATMAddress - This is the full address of the service.
The ATM client will use this address to establish a connection
with the service.

atmfSrvcRegAddressIndex - An arbitrary integer to differentiate
multiple rows containing different ATM addresses for the same
service on the same port.

atmfSrvcRegParm1 - An octet string whose size and meaning is
determined by the value of atmfSrvcRegServiceID.

The service registry table is indexed by atmfSrvcRegPort,
atmfSrvcRegServiceID and atmfSrvcRegAddressIndex.

3.1 Service Parameter String

A generic parameter string is defined in the service registry table,
thus allowing protocol-specific parameters to be specified. To be
consistent with [1], the parameter string for NHRP shall be:

ar$pro.type 16 bits Protocol type
ar$pro.snap 40 bits Optional extension to protocol type
ar$plen 8 bits Length of protocol address
ar$addr plen octets Network address
ar$mask plen octets Network mask

Where

ar$pro.type - See [1]. (IPv4 is 0x0800, IPv6 is 0x86DD)

ar$pro.snap - See [1]. (IPv4 and IPv6 are 0)

ar$plen - Length of the protocol address.
(IPv4 is 4, IPv6 is 16)

ar$addr - Network address represented in network byte
order

ar$mask - Network mask represented in network byte order

3.2 Service Object Identifier

This OID, assigned in the ATM Forum Service Registry MIB, names
ATMARP within the context of server discovery.

atmfSrvcRegNHRP OBJECT IDENTIFIER ::= { 1.3.6.1.4.1.353.1.5.5 }

It does not name any managed objects, rather is used to locate
appropriate rows in the service registery table.

4. Next Hop Client Behavior

An Next Hop Client NHC) will access the service registry table via
ILMI using the SNMP GetNext operator to "sweep" (SNMP parlance for a
linear search) beginning with {Port = 0, ServiceID = <see Section
3.2>, Index = 0} while holding the port number and the serviceID
constant. (Port number 0 is used within ILMI to indicate "this
port.")

An NHC with no local configuration, such as a diskless workstation,

must use the row with the lowest index value if multiple Next Hop
Server (NHS), possibly for multiple networks, are listed.

NHC that have local IP configuration must use a row that has the
appropriate IP address. For example, consider the case where an IP
router has 3 logical interfaces defined on a single physical
interface with IP addresses 1.0.0.1/8, 128.10.0.1/16 and
171.69.150.226/24. The router will sweep the service registry table
looking for rows that have atmfSrvcRegParm1 values as shown below:

Net number/mask atmfSrvcRegParm1
---------------- --------------------------------------------------
1.0.0.0/8 08 00 00 00 00 00 00 04 01 00 00 00 ff 00 00 00
128.10.0.0/16 08 00 00 00 00 00 00 04 80 0a 00 00 ff ff 00 00
171.69.150.0/24 08 00 00 00 00 00 00 04 ab 45 96 00 ff ff ff 00

When the correct atmfSrvcRegParm1 values are located, the router may
then establish an SVC to the selected NHS and perform the appropriate
protocol operations.

Redundant NHS are supported with multiple rows in the service
registry table. This list of NHS is ordered with the primary NHS
having the lowest index value. The NHC must attempt to utilize the
primary NHS before utilizing a secondary NHS. Administrators must
ensure that the listed NHS are synchronized.

5. NHRP Server (NHS) Behavior

A Next Hop Server (NHS) shall be locally configured. The NHS may
retrieve the NHRP service registry data to validate the results. If
an incorrect row is retrieved the error may be flagged in a locally
significant way.

6. Relationship with PNNI Augmented Routing

An augmented version PNNI ("PNNI Augmented Routing," or PAR) [3] has
been developed by the ATM Forum. PAR can distribute data such as NHS
addresses. Further, the ATM Forum is developing a proxy mechanism for
PAR (Proxy PAR) that would allow a UNI-attached host or router to
access PAR data without a full PAR implementation.

These mechanisms offer a promising way to manage the service registry
tables maintained on each switch in an ATM network, yet would not
require changes to the mechanism defined in this memo. Hosts and
routers can continue to utilize ILMI-based or Proxy PAR-based server
discovery and network administrators could manage the service
registry data with local configuration or via PAR and Proxy PAR.

7. Security Considerations

The server discovery mechanism is built on the ILMI managment
framework and the security embodied in that framework. Access, to
user- or network-side information is controlled by MIB design rather
than protocol security mechanisms.

The service registery MIB, the table containing information for
server discovery, is defined in [2] with read-only access. This means
that any user-side device may query the service registry, but may not
modify the service registry via ILMI. Instead, the sevice registry
table must be modified via local configuration on the ATM switch.

References

[1] Luciani, J., et al., "NBMA Next Hop Resolution Protocol", RFC
2332, April 1998.

[2] ATM Forum, "Integrated Local Management Interface (ILMI)
Specification Version 4.0," af-ilmi-0065.000, September 1996.

[3] ATM Forum, "PNNI Augmented Routing (PAR) Version 1.0," af-ra-
0104, January 1999.

Author's Address

Mike Davison
Cisco Systems
170 West Tasman Drive
San Jose, California 95134

Phone: (408) 526-4000
EMail: mike.davison@cisco.com

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