Use of command tunnel path-mtu-discovery

[mahesh18]

                   Hi Everyone,

Need to know why we have to use the command tunnel path-mtu-discovery  if we have GRE tunnels at both ends?

Also can the same command be used if we have GRE  over IPSEC VPN?

Thanks

MAhesh

[Marcin Latosiewicz · Accepted solution]

You can read the description here:

http://www.cisco.com/en/US/docs/ios-xml/ios/interface/command/ir-t2.html#GUID-3B831D75-DAD0-472A-AC32-A6A066F71C33

It forces unreachables to be sent should we exceed MTU, rather fragmentation to occur.

And yes it applies to GRE over IPsec and is quite a good feature in most cases.

[mahesh18]

Hi MArcin,

Thanks for reply.

I was seeing packet drops between 2 GRE tunnels and once i config this command then

Total output drops: 0

Do you see this behaviour when you config above command it does not do output drops?

Thanks

mahesh