Re: Inconsistency in packet drop due to MTU (eth vs veth)

[Eric Dumazet]

On Thu, 2017-01-19 at 17:41 +0100, Fredrik Markstrom wrote:
> Hello,
> 
> I've noticed an inconsistency between how physical ethernet and veth handles mtu.
> 
> If I setup two physical interfaces (directly connected) with different mtu:s, only the size of the outgoing packets are limited by the mtu. But with veth a packet is dropped if the mtu of the receiving interface is smaller then the packet size. 
> 
> This seems inconsistent to me, but maybe there is a reason for it ? 
> 
> Can someone confirm if it's a deliberate inconsistency or just a side effect of using dev_forward_skb() ?

It looks this was added in commit
38d408152a86598a50680a82fe3353b506630409
("veth: Allow setting the L3 MTU")

But what was really needed here was a way to change MRU :(