IS IS Summarization


Summarization is an optimization feature, to limit the flooding of prefixes, filter component routes and hide instability within an area.


  • Summarization can be configured on L1/L2 routers for natively advertised routers.
  • It can be summarized in two directions:
    • L1 into L2 area.
    • L2 into L1 area.
  • Summarization within L1 is not possible by default. The only way to accomplish that is by redistributing at a L1 router and summarizing at the same time. Make sure to specify that it is a L1 route during redistribution.
  • Summarized routes will be suppressed (component routes).

Relevant Commands


R1(config-router)#        summary-address (net) (subnet) [level-1 | level-2 | level-1-2] [tag] [metric]


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