GRE tunnel MTU and bandwidth

[mahesh18]

                   Hi Everyone.

GRE tunnel from Site A has

MTU 17916 bytes, BW 100 Kbit, DLY 50000 usec,

Site B has

MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,

I read that default BW for GRE is 9kbit  but here 1 side has default and other side has 100.

One side has default MTU other side has 17916

so is this normal behaviour?

So need to know the purpose of using MTU 17916 and bandwidth of 100  on Site A?

Thanks

Mahesh

[shamax_1983]

Hello Mahesh,

The bandwidth and Delay on the Tunnel interface is sometimes used to change the EIGRP metrics to influence routing table. For example if you have two equal cost paths to certain network in your routing table, you can increase the delay on one of the tunnels and make the other tunnel the preffered one. Not sure if this is the case with your setup.. it;s really hard to say without looking at the config.

As for the MTU, not sure why MTU size is 17916..  1514 make sense but still too big for a GRE tunnel.. I think

Please rate this post if helpful.. THanks

[mahesh18]

Hi Shamal,

When i check the config of tunnel interface there is  no bandwidth command configured.

So do you thing it can be due to IOS as both devices have different IOS version.

MTU 17916 bytes, BW 100 Kbit, DLY 50000 usec has IOS --cat4500-ipbasek9-mz.122-53.SG.bin

Other side is cat4000-i9k91s-mz.122-25.EWA10.bin

Thanks

Mahesh