MTU

Baldur Norddahl baldur.norddahl at gmail.com
Fri Jul 22 12:01:36 UTC 2016


Hi

What is best practice regarding choosing MTU on transit links?

Until now we have used the default of 1500 bytes. I now have a project were
we peer directly with another small ISP. However we need a backup so we
figured a GRE tunnel on a common IP transit carrier would work. We want to
avoid the troubles you get by having an effective MTU smaller than 1500
inside the tunnel, so the IP transit carrier agreed to configure a MTU of
9216.

Obviously I only need to increase my MTU by the size of the GRE header. But
I am thinking is there any reason not to go all in and ask every peer to go
to whatever max MTU they can support? My own equipment will do MTU of 9600
bytes.

On the other hand, none of my customers will see any actual difference
because they are end users with CPE equipment that expects a 1500 byte MTU.
Trying to deliver jumbo frames to the end users is probably going to end
badly.

Regards,

Baldur



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