We would be irresponsible as network designers if we did not study and appreciate IS-IS for the problems it can solve. IS-IS is a link-state protocol similar to OSPF. IS-IS uses TLVs (similar to BGP), and is thus easily extended. IS-IS and OSPF are the two choices you have when deploying TE on MPLS networks, so you should know how IS-IS compares with OSPF when your design requires fast convergence. Cisco has several resources on their site, which I’ve distilled into a few rules of thumb:
- Increase LSP refresh timer to a high value
- Increase MAX LSP lifetime to a high value
- Tune PRC interval
- Tune SPF interval
- Tune LSP generation interval
- Use BFD in lieu of fast hellos (on multiaccess networks)
- Tune ISIS retransmit interval
- Set overload-bit on startup
- Disable hello padding
- Use a single IS type where possible (note that Cisco default is L1/L2)
- Use metric-style wide (not necessarily FC related, but is req’d for TE)
Also related: use isis mesh-group and configure point-to-point interface type on multiaccess interfaces where they are really point-to-point (think 2-member Ethernet segments).
References:
Cisco Technology Support Page
Cisco IOS 12.4 IS-IS Fast Convergence
Cisco Configuration Example
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