Re: IS-IS Flat Network Size

[Mark Tinka via NANOG <nanog () lists nanog org>]

On 27/07/2026 19:08, Tom via NANOG wrote:

> Hello,
>
> I'm wondering what some practical/real experiences have been with building out a large flat IS-IS network. I've read a lot 
> of threads on conjecture and older docs on what the vendors recommend but haven't found anything yet or real world examples. Two 
> questions,
>
> 1) Is anyone running a flat IS-IS L2 network with approx 300 routers? If not, what is the higher end you've seen?
> 2) On aggregation routers, what is the upper end of IS-IS adj to downstream routers? Would agg routers with approx 100 
> connections be an issue moving to IS-IS with the addition of keeping track of that many adj?

With today's control planes, 300 nodes is not even a corn flake :-).

We did that number back in 2009, on Cisco CRS-1's, ME3600X's and Juniper 
M320's, T320's and MX480's.

The state-of-the-art has moved on a great deal, since then.

Mark.
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