MTU handling in 6RD deployments

Mark Townsley mark at
Fri Jan 17 09:40:35 CET 2014

On Jan 17, 2014, at 9:24 AM, Mikael Abrahamsson wrote:

> On Thu, 16 Jan 2014, Templin, Fred L wrote:
>> The key is that we want to probe the path between the BR and CE (in both directions) *before* allowing regular data packets to flow. We want to know ahead of time whether to allow large packets into the tunnel or whether we need to shut the MTU down to 1480 (or 1472 or something) and clamp the MSS. Because, once we restrict the tunnel MTU hosts will be stuck with a degenerate MTU indefinitely or at least for a long time.
> This method makes some sense, but since network conditions can change, I would like to see periodic re-checks of the tunnel still working with the packet sizes, perhaps pinging itself over the tunnel once per minute with the larger packet size if larger packet size is in use.

Section 8 of RFC 5969 could be relevant here.

- Mark

> -- 
> Mikael Abrahamsson    email: swmike at

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