I use MTU 9000* on all my router-to-router links because I need to be able to carry larger-than-1500-byte circuit traffic. If nothing else, circuit VLANs all need to be a bit over 1500 bytes on the outside (i.e. with my tags and possibly tags of other carriers involved) so that they are 1500 bytes on the inside. * Maybe I should/will-need-to change this to 9000 + a bit to allow for 9000 inside.

We don't typically see carriers looking for anything greater than about 2000 bytes in practice, though we also follow a similar 9000 byte configuration on our internal transport links. 1500 to the internet edge. You could fiddle with the MTU to eek out a few extra bytes for circuits, but what you're doing today already ~4x the real world use cases that we've seen. 

Maybe experiences differ for providers that carry a lot of traffic between data centers. 

Ben Wiechman

Director of IP Strategy and Engineering

320.247.3224 | ben.wiechman@arvig.com

Arvig | 224 East Main Street | Melrose, MN 56352 | arvig.com




On Fri, Jun 18, 2021 at 2:53 PM Richard Laager <rlaager@wiktel.com> wrote:
On 6/18/21 2:16 PM, Jonathan Stewart wrote:

Finally, views do differ, i'm sure others have opinions that do not match mine.

I don't see anything wrong in what you said. I'll add some detail on what we're doing in case it's helpful (or if someone can educate me if I'm doing something bad):

I use MTU 9000 on my transit connections, coordinated with the transit provider, because there seems to be no harm in doing that.

I use MTU 9000* on all my router-to-router links because I need to be able to carry larger-than-1500-byte circuit traffic. If nothing else, circuit VLANs all need to be a bit over 1500 bytes on the outside (i.e. with my tags and possibly tags of other carriers involved) so that they are 1500 bytes on the inside. * Maybe I should/will-need-to change this to 9000 + a bit to allow for 9000 inside.

I'm 1500 bytes at the customer edge for Internet. I'm also 1500 bytes at IXes.

-- 
Richard

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