IP MTU on gif and gre interfaces (with and without IPSec encryption)

[Victor Sudakov]

Victor Sudakov wrote:
> 
> If the MTU on the external Ethernet interface is 1500, it should be safe
> to configure the gif(4) interfaces with mtu=1480 and gre(4)
> interfaces with mtu=1476, correct?
> 
> I've noticed that a newly created gre0 interface has the expected "mtu 1476"
> value, but a newly created gif0 interface has "mtu 1280", why would the
> default be so low?
> 
> A second question. If the gif and gre tunnels will be wrapped in
> IPSec transport mode, does it make sense to set the MTU on the
> corresponding gif and gre interfaces to some lower value?

And to make the matter even more mysterious, if_ipsec(4) which is
essentially the same as gif, is created by default with mtu=1400 for
some reason.

-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
2:5005/49 at fidonet http://vas.tomsk.ru/
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