Bridge netfilter MTU discovery

[Patrick McHardy]

Stephen Hemminger wrote:
> Is there an easy way to force bridge packets to cause an ICMP frag needed
> if the MTU of the destination is too small. Normal bridging will just drop
> the packet, but a rule to send ICMP would allow PMTU to work. Maybe even
> having a module to fragment would be good.

Conntrack breaks PMTU discovery by always defragmenting/refragmenting
packets, regardless of IP_DF. But there is no way to generate ICMP
frag required messages using iptables.