Enterasys Networks X-PeditionTM manual Ospf Troubleshooting, Null Interface, Route Preference

IP Routing Protocols

OSPF Troubleshooting

XSR commands provide debugging of OSPF Version 2 control information including:

•Monitoring specific OSPF events from the CLI with show ip ospf (with debugging enabled)

•Control Packets with debug ip ospf packet

•LSA transmissions/receptions with debug ip ospf lsas

•Neighbor Events with debug ip ospf nbr

•Designated Router Events with debug ip ospf dr

Be aware that only one CLI debug session is permitted at a time.

Null Interface

The XSR provides a non-configurable null interface (null 0) so that discard routes can be installed for OSPF LSA Type 3 and 5 route summarization. The null interface acts as a “bit bucket” to dispose of unwanted packets while avoiding the problem of looping.

The null interface is unlike any other XSR port in that it does not need an IP interface to be enabled

-it is always up, it cannot be deleted, and it appears only when specifically referenced by the show ip interface null0 or show interface null0 commands. Other show commands do not display the port. Additionally, the null interface is characterized by the following:

•It can be specified in the ip route command as the next hop: ip route 7.0.0.0 255.0.0.0 null0

•Routes which are unreachable through null0 cannot be redistributed

•It responds to the interfaces.ifTable.ifEntry SNMP query with the value 0 or as follows: interfaces.ifTable.ifEntry.ifDescr.7 = Null0

Refer to the XSR CLI Reference Guide for more information on commands.

Route Preference

Route preference or administrative distance is a tool to decide which route to install in the global routing table. Each routing protocol presents the global Routing Table Manager (RTM) with its best selection of a route. If several routes to the same destination are offered (derived from different protocols), installation occurs based on the protocol’s administrative distance. The route for the protocol with the lowest distance is chosen from the table. The feature functions as follows:

•Administrative distance is configurable per protocol using the distance command. Static routes remain configurable per route.

•OSPF distance can be set for different values on intra-area, inter-area, and external routes.

•OSPF distance must follow this rule: Intra-area distance is less than inter-area distance which is less than external distance.

•Static route distance can be set using the ip route command. If distance is not specified, the default distance is applied.

•Aggregation is not accepted in order to set the distance for several static routes at one time.

•Configuring the same distance across different protocols is permitted except for multiple static routes. Tie breaks are resolved by the following default administrative distances:

– Connected routes: 0

XSR User’s Guide 5-17