topic Re: about mtu in General Topics

about mtu

PanIst — Tue, 16 Aug 2016 20:38:51 GMT

Hello all,

There is a problem with a smb traffic(very very slow)

For the related source and dest. ip address 2 filter is configured and show counter output has :

flow_fwd_mtu_exceeded 9 3 info flow forward Packets lengths exceeded MTU
flow_ipfrag_frag 18 6 info flow ipfrag IP fragments transmitted

There is no drop.

All devices through the way has mtu as 1500 like paloalto.

Any idea ?

Thanks

Re: about mtu

reaper — Tue, 16 Aug 2016 22:17:29 GMT

are you absolutely sure there is no device in the middle that may have a lower (even very slightly) or, in this case more likely, higher MTU ? the global counters indicate fragmentation is happening because the interface's MTU is exceeded: if the firewall is set to 1500 and this traffic is not traversing a VPN, the firewall is reciving packets larger than 1500 (minus space for headers etc)

you can try enabling TCP MSS adjust on the interface advanced tab, which could regulate mss/mtu in the communication