RE: [Xen-users] Do bridges or vif defragment IP-packets?

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> 
> When we send an ICMP-packet with 6400 data-bytes (ping -s 6400 -c 1
> 192.168.39.1) from Linux-guest connected to "vif9.1" to
> the other linux-guest connected to "vif2.1" we see with tcpdump
connected to
> intbr1, that some instance (intbr1? vif9.1) defragmented
> the 5 ip-packets from vif9.1 into 1 ip-packet, though mtu-size for the
vif-
> interfaces, intbr1 and eth-interfaces of the guests
> are all set to 1500 bytes:

What did you expect to happen? If the MTU is 1500 bytes then by
definition, no larger packet will be allowed through (TCP is an
exception to this where LSO/TSO/GSO is supported)

If the 'do not fragment' flag is not set on the icmp packet then the IP
layer on the sending host will fragment the packet at the IP level.

If the 'do not fragment' flag is set then the sending host will respond
with an icmp 'fragmentation required' packet.

James


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