Ospf Overview; Circuitless Ip (Clip) - Avaya 8600 Engineering

1. OSPF Overview

Open Shortest Path First is a link state protocol designed as a standards based Internal Gateway
Protocol (IGP) for the purpose of interconnecting users and networks. OSPF maintains a link state
database of interface, link, router, and network status in order to calculate the shortest path to each and
every network element. From the link state database, a routing table is built. This calculation is based on
Dijkstra‟s model of calculating the shortest path from one point to another.
OSPF Standards supported on Ethernet Routing Switch 8600
The Ethernet Routing Switch 8600 supports the following standards:

RFC 1253 (OSPF MIB)

RFC 1583 (OSPF version 2)

RFC 2178 (OSPF version 2)

RFC 1850 (OSPF Management Information Base)

RFC 2178 (OSPF MD5 cryptographic authentication)
Dijkstra's Algorithm
This calculation is used to determine the best path to any network based on the total path cost. All paths
to a given network are determined and the cost calculated, however, only the best path will be used
populate the routing table.

2. Circuitless IP (CLIP)

A Circuitless IP address, sometimes referred to as a loopback address, is an IP address that is not tied to
any specific interface. Since it is not tied to a physical port or VLAN, its state is always active. It is highly
recommended to use the Circuitless IP address for the OSPF Router-ID. By doing so, the OSPF Router-
ID is always active regardless of any port state (up/down).
To configure CLIP and use it for the OSPF Router-ID, the following commands are used.
Step 1 Configure a Circuitless IP address
config ip circuitless-ip-int
<ipaddress/mask>
config ip circuitless-ip-int
enable
Step 2 Enable OSPF
config ip ospf admin-state enable
config ip ospf router-id <CLIP IP Address>
config ip ospf enable
November 2010
X create
X ospf
ERS 8600 / 8800 OSPF Technical Configuration Guide
This step creates a circuitless IP address which will be
used for the OSPF Router-ID where X is the CLIP ID and
can be any instance from 1-32. The CLIP IP address
typically uses a 32-bit mask.
These commands enable OSPF and set the OSPF
Router-ID using Circuitless IP created in Step 1.
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