Common operational misconceptions

George Bonser gbonser at
Fri Feb 17 16:10:37 UTC 2012

> It depends on how you define "work well".
> As the RFC says:
>    indication of some significantly disruptive event in the network,
>    such as a router failure or a routing change to a path with a
> smaller
>    MTU.
> it can not react against PMTU changes very well.
> It is seemingly working well means there is not much PMTU changes,
> which means we had better assumes some PMTU (1280B, for example) and
> use it without PMTUD.
> 						Masataka Ohta

It depends on the OS and the method being used.  If you set the option to "2" on Linux, it will do MTU probing constantly and react to MTU changes.  Also, the MTU for a given path only "lives" for 5 minutes anyway (by default) and is "rediscovered" with Linux.   (value in /proc/sys/net/ipv4/route/mtu_expires) but other operating systems may behave in other ways.

I agree that if one tries hard enough, they can ensure a broken path and there are always people who seem to devote a lot of energy to that end.  There's nothing that can be done about them but there is much the OS can try to do to defeat them at their task.

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