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    SubjectInconsistency in packet drop due to MTU (eth vs veth)
    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() ?

    Example:

    Using physical interfaces
    =================
    client> ip link set dev eth0 mtu 500
    server> ip link set dev eth2 mtu 1500
    server> ping -qc 2 -s 600 client
    PING 135.15.35.74 (135.15.35.74) 1100(1128) bytes of data.
    --- 135.15.35.74 ping statistics ---
    2 packets transmitted, 2 received, 0% packet loss, time 999ms
    rtt min/avg/max/mdev = 0.818/0.864/0.910/0.046 ms

    Using veth
    =============
    server> ip netns add clientns
    server> ip link add name serverif type veth peer name clientif
    server> ip addr add 10.0.0.1/24 dev serverif
    server> ip link set serverif mtu 1500 up
    server> ip link set clientif up netns clientns
    server> ip netns exec clientns ip link set clientif mtu 500
    server> ip netns exec clientns ip addr add 10.0.0.74/24 dev clientif
    server> ping -qc 2 -s 600 10.0.0.74
    PING 10.0.0.74 (10.0.0.74) 600(628) bytes of data.
    --- 10.0.0.74 ping statistics ---
    2 packets transmitted, 0 received, 100% packet loss, time 1008ms

    /F

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