ISIS route summarization

Ivan Pepelnjak ip at
Tue Feb 24 10:00:44 UTC 2009

The short answer is "NO". L2 IS-IS is a single SPF domain and all routers
are supposed to have identical view of the network. If you want
IS-IS-provided aggregation, you need to use L1 and L2. 

There are only two protocols that allow unlimited levels of aggregation: BGP
and EIGRP :)


> -----Original Message-----
> From: Jack Bates [mailto:jbates at] 
> Sent: Monday, February 23, 2009 10:26 PM
> To: nanog at
> Subject: ISIS route summarization
> In a level2 only ISIS network (not using multiple areas due 
> to MPLS limitations), is there a better method for handling 
> aggregate routes than creating an aggregate and 
> redistributing it into ISIS for each router? Primarily 
> Cisco/Juniper based. Cisco I believe has an aggregate option 
> in ISIS (similar to OSPF) and Juniper has a separate 
> aggregate function which can be distributed into ISIS. 
> Neither can do summarization per say unless they cross 
> between levels; unless I'm mistaken.
> Offlist input is fine. Just trying to double check my brain 
> while setting up IPv6 on the access edges.
> Link state does have it's limitations. ;)
> -Jack

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