On 23 July 2016 at 10:28, Tore Anderson <tore@fud.no> wrote:
* Baldur Norddahl
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.
You use case as described above puzzles me. You should already your peer's routes being advertised to you via the transit provider and vice versa. If your direct peering fails, the traffic should start flowing via the transit provider automatically. So unless there's something else going on here you're not telling us there should be no need for the GRE tunnel.
I did not say we were doing internet peering... In case you are wondering, we are actually running L2VPN tunnels over MPLS. Regards, Baldur