IS-IS Errors

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This section reviews just a couple of typical errors encountered in IS-IS routing environments. Example 11-30 describes a situation in which the IS-IS process receives a hello packet that is only 51 bytes instead of the expected 53 bytes ATM cell . This is caused by packet corruption most likely because of malfunction of some interface hardware. This might result in adjacency failures if too many consecutive hellos are corrupted in this manner.

Example 11-30 Unexpected Hello Packet Size
 Nov 16 02:18:04.848 EDT: %CLNS-4-BADPACKET: ISIS: P2P hello, option 8 length 53         remaining bytes (51) from VC 2 (ATM4/0.2) 

Example 11-31 indicates an incorrectly formatted link-state packet in which an NSAP address length appears longer than expected. This could be caused by software implementation bugs and might have an effect on the dissemination of routing information.

Example 11-31 Unexpected NSAP Address Length in Incorrectly Formatted LSP
 Mar 10 11:59:46.171: %CLNS-3-BADPACKET: ISIS: L1 LSP, option 1 address prefix length         135 > max NSAP length (21), ID 0000.0000.04B7.00-00, seq 25948, ht 1115 from         *PPP* (POS6/0). 

The router-level command log-adjacency-changes causes logging of adjacency changes, as shown in Example 11-32.

Example 11-32 Tracking Adjacency Changes
 RT1#  show logging  %CLNS-5-ADJCHANGE: ISIS: Adjacency to 0000.0000.0001 (ethernet 0)  %CLNS-5-ADJCHANGE: ISIS: Adjacency to 0000.0000.0002 (ethernet 0) 

Example 11-33 shows the type of message logged when a router determines that there is another router in the same area or backbone with a duplicate of its system ID.

Example 11-33 Duplicate System ID Message
 RT1#  show logging  %CLNS-4-DUPSYSTEM: ISIS: possible duplicate system  ID 0000.0000.0002 detected 
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Troubleshooting IP Routing Protocols
Troubleshooting IP Routing Protocols (CCIE Professional Development Series)
ISBN: 1587050196
EAN: 2147483647
Year: 2002
Pages: 260

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