Troubleshooting Guide

Table Of Contents
4. Ensure the multicast address of 224.0.0.5 can traverse the link. If multicast traffic is blocked,
you must configure the Avaya Virtual Services Platform 4000 Series for OSPF nonbroadcast
multiaccess (NBMA) instead of broadcast.
Example
VSP-4850GTS> enable
VSP-4850GTS# trace level 6 2
VSP-4850GTS# trace screen enable
Troubleshooting OSPF ExStart/Exchange problems
Before you begin
You must log on to Interface Configuration mode in ACLI.
About this task
Although both devices can recognize each other and move beyond 2-way state, the devices can
become stuck in the ExStart/Exchange state. A mismatch in maximum transmission unit (MTU)
sizes between the devices usually causes this type of problem. For example, one device can use a
high MTU size and the default value on the other device is a smaller value. Depending on the size of
the link state database (LSDB), the device with the smaller value cannot process the larger packets
and remains in ExStart/Exchange state. This problem is usually encountered during interoperations
in networks with other vendor devices.
In Virtual Services Platform 4000, the supported MTU size for OSPF is 1500 bytes by default.
Incoming OSPF database description (DD) packets are dropped if their MTU size is greater than
1500 bytes.
If you configure the device to ignore the MTU size, the device does not perform the MTU check on
the incoming OSPF DD packet. Virtual Services Platform 4000 automatically checks for OSPF MTU
mismatches.
Procedure
1. View the OSPF packets:
trace level 6 2
2. Ensure that the MTU size value for both devices match.
3. Configure the interface to accept OSPF DD packets with a different MTU size:
ip ospf mtu-ignore enable
Example
VSP-4850GTS> enable
VSP-4850GTS# configure terminal
VSP-4850GTS(config)# interface vlan 100
Troubleshooting OSPF ExStart/Exchange problems
January 2017 Troubleshooting 259
Comments on this document? infodev@avaya.com