Troubleshooting the Intermediate System to Intermediate System (IS-IS) Protocol
Troubleshooting issues with the Intermediate System to Intermediate System (IS-IS) protocol is once again pursued thru an investigation of the show and debug commands and their options.
Viewing the show options
To start, here are the different options available in the show command:
Router2>enable Password: Router2#show isis ? * All IS-IS address families database IS-IS link state database hostname IS-IS Dynamic hostname mapping ipv6 IS-IS IPv6 lsp-log IS-IS LSP log mesh-groups IS-IS mesh groups mpls IS-IS MPLS neighbors IS-IS neighbors rib ISIS local RIB information route IS-IS level-1 routing table spf-log IS-IS SPF log topology IS-IS paths to Intermediate Systems
Among these options are several with useful information, most notably database, neighbors, route, and topology.
The output of the topology command is shown, notice that it includes both Level 1 and Level 2 routers, which both of the referenced routers are members of, because they were created with the default options on router isis. Router2 sees that the router Router1 is found on interface Fa0/0. So, with the topology command, you can see neighbors and further, whereas the neighbors command would only show adjacent routers.
Router2>enable Password: Router2#show isis topology IS-IS paths to level-1 routers System Id Metric Next-Hop Interface SNPA Router2 -- Router1 10 Router1 Fa0/0 0017.e0c9.b7b0 IS-IS paths to level-2 routers System Id Metric Next-Hop Interface SNPA Router2 -- Router1 10 Router1 Fa0/0 0017.e0c9.b7b0
Looking at debug options
Finally, you look at the debug options, which are similar to the Open Shortest Path First (OSPF) debug command. Depending on the types of problems you are experiencing, you may want to focus on different parts of the IS-IS protocol, such as adj-packets, protocol-errors, or spf-statistics.
Router2>enable Password: Router2#debug isis ? adj-packets IS-IS Adjacency related packets authentication IS-IS packet authentication checksum-errors IS-IS LSP checksum errors local-updates IS-IS local update packets mpls IS-IS MPLS nsf IS-IS Non-Stop Forwarding protocol-errors IS-IS LSP protocol errors rib IS-IS IP Routing Information Base snp-packets IS-IS CSNP/PSNP packets spf-events IS-IS Shortest Path First Events spf-statistics IS-IS SPF Timing and Statistic Data spf-triggers IS-IS SPF triggering events update-packets IS-IS Update related packets