Path MTU discovery on physical interface

[sandip_ray]

Can Path MTU discovery be configured on a physical interface like tunnels interfaces '

 tunnel path-mtu-discovery" ?

I know we can configure "ip tcp path-mtu-discovery" as a global config command but why not on a physical interface?

[pman · Accepted solution]

Hi,

you set the tunnel path-mtu-discovery command under interface configuration mode

You can solve the GRE-related problems by manually lowering the ip mtu on the tunnel interface (ideally in combination with the ip tcp adjust-mss configuration command), or you could enable PMTUD for GRE tunnels with the tunnel path-mtu-discovery interface configuration command. When you enable the PMTUD on a GRE tunnel, the GRE packets are sent with the DF bit set and the router responds to the incoming ICMP destination unreachable messages with the reduction of the tunnel MTU size

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/interface/command/ir-cr-book/ir-t2.html#wp1581717163 

about the ip tcp path-mtu-discovery command:

this command designed To enable the Path MTU Discovery feature for all new TCP connections initiated by the router when the router is acting as a host (for example: BGP and Telnet)

[sandip_ray]

thanks Mr. pman. I get what you are saying but my question is little different. In case of a GRE we can do "tunnel path-mtu-discovery". But is there a way to do the same on my physical Gig0/0/0 egress interface instead of global config command "ip tcp path-mtu-discovery" ..

[sandip_ray]

thank you @pman for further details. Appreciate it. 

[MHM Cisco World · Accepted solution]

path mtu discover under tunnel is acceptable because we specify the destination as well as source.
but with case of interface we only have ip address of interface without know the destination this is why not acceptable for interface. 

[sandip_ray]

Makes sense @MHM Cisco World : I thought of it once but wasn't sure. Thank you for taking your time reading my question and responding it. Appreciate it.