Introduction

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

Summarization

• 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).

router isis
 summary-address 55.0.0.0 255.0.0.0 level-1
 redistribute connected level-1

router isis
 summary-address 4.4.0.0 255.255.0.0    ! <--- default to Level 2
 summary-address 6.6.0.0 255.255.0.0 level-1

Relevant Commands

summary-address

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

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