Internet-Draft Mike Davison
Cisco Systems
Oct 15, 1998
ILMI-Based Server Discovery for NHRP
<draft-ietf-ion-discov-nhrp-02.txt>
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Abstract
This memo defines how ILMI-based Server Discovery, which provides a
method for ATM-attached hosts and routers to dynamically determine
the ATM address of servers, shall be used to locate NHRP servers.
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1. Introduction
Presently, configuring a host or router to use NHRP [1] is cumbersome
and error-prone since it requires at least one ATM addresses 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 Service Registry MIB, as defined by the ATM
Forum, is provided in this memo. The reader should consult [2] for a
complete description of this MIB, but the information contained here
is sufficient for an understanding of its use to support NHRP server
discovery.
2. 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 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 which
uniquely identifies the type of service at the address
provided in the table. (See Appendix for NHRP OID.)
atmfSrvcRegATMAddress - This is the full address of the service.
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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.
2.1 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:
mar$pro.type 16 bits Protocol type
mar$pro.snap 40 bits Optional extension to protocol type
mar$plen 8 bits Length of protocol address (a)
mar$addr a octets Network address
mar$mask a octets Network mask
Where
mar$pro.type - See [1]. (IPv4 is 0x0800, IPv6 is 0x86DD)
mar$pro.snap - See [1]. (IPv4 and IPv6 are 0)
mar$plen - Length of the protocol address.
(IPv4 is 4, IPv6 is 16)
mar$addr - Network address represented in network byte
order
mar$mask - Network mask represented in network byte order
2.2 Service Object Identifier
This OID, assigned in the ATM Forum Service Registry MIB, names
ATMARP within the context of server discovery.
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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.
3. 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 Appendix>,
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 a 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 via [3].
4. 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
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an incorrect row is retrieved the error may be flagged in a locally
significant way.
5. Relationship with PNNI Augmented Routing
An augmented version PNNI ("PNNI Augmented Routing," or PAR) [4] is
being 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) [5] 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.
6. Security Considerations
The server discovery mechanism is intended for environments where a
given ATM switch and its attached hosts or routers are in the same
administrative domain, hence no authentication is required.
References
[1] Luciani, J., et al., "NBMA Next Hop Resolution Protocol,"
<draft-ietf-rolc-nhrp-11.txt>, March, 1997.
[2] ATM Forum, "Integrated Local Management Interface (ILMI)
Specification Version 4.0," af-ilmi-0065.000, September, 1996.
[3] Luciani, J., and Fox, B., "A distributed NHRP Service Using
SCSP," <draft-ietf-ion-scsp-atmarp-00.txt>, April, 1997.
[4] Callon, R., et al., "An Overview of PNNI Augmented Routing,"
ATM-Forum 96-0354, April, 1996.
[5] Droz, P., Przygienda, T., "Proxy PAR,"
<draft-ietf-ion-proxypar-arch-00.txt>, March, 1998.
Author's Address
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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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