IS-IS on FRR - Is Anyone Running It?

Mark Tinka mark.tinka at
Mon Apr 6 08:58:21 UTC 2020

On 6/Apr/20 09:58, Radu-Adrian Feurdean wrote:

> I won't speak for Mark, but NO, when you're carrying somebody's else's traffic you do your best to have the MTU on each and every backbone link "high enough" : preferably in the 9200(bytes) range, so you can easily transport 9000(bytes) client packets, and by no means so small that you need to fragment 1500(IP)/1514(Eth) byte packets. If things are really-really bad, 1600 bytes towards the edge.

Yes, this.

Within our core, we run 9,178 bytes (which translates to 9,192 bytes on
Junos and IOS XR), to support the transport of Jumbo frames for
customers that need it, typically l2vpn type services.

If VMware ESXi did not limit itself to 9,000 bytes, we wouldn't have
needed to set the IS-IS MTU at all, as it would have been inferred from
the physical interface of each device.

> Back to the original question, I would expect FRR to be able to manually specify a MTU/frame-size, like any other decent NOS (even if it's not a full NOS).

One would have thought.

Even if no one is running it, I'd have assumed the developers would have
said something. My Google-fu is generally okay, but not on this one :-).


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