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Beginner

ISIS

In ISIS, by default will ISIS L1 routes gets advertised into L2 area or L2 routes gets advertised into L1 area?

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Hall of Fame Master

Hello @Aneek ,

on an L1/L2 node the L1 routes can be injected into L2. The routes passed from L1 to L2 should have an UP flag set to signal this fact.

The opposite does not happen by default as routing outside an ISIS area can use the attach ATT bit on the L1/L2 nearest router.

In some cases to avoid some sub optimal routing some L2 routes can be leaked into L1 with a down bit flag set to avoid re-injection into L2.

 

Hope to help

Giuseppe