Bandwidth used by Tunnels

[olorunloba]

I am wondering what is the amount (and the manner to tweak it) of bandwidth used by GRE Tunnels i.e. by its keepalives, to maintain the tunnel interface up. I have configured tunnels over some slow serial links, and I'm wondering whether the tunnels itself could be eating up the bandwidth, and whether it might just be better to use static routing throughout the whole hop.

[rais]

GRE Keepalives are optional and their rate can be set by using keepalive command. Here is a link that may be helpful:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t8/grekpliv.htm#1024997

You can also use SNMP to reveal bandwith-usage across the tunnel.

Thanks.

[olorunloba]

Ok, what I'm really interested in knowing is the amount of overhead of using the tunnels. Are you saying that by setting no keepalives, there will be no overheads?

[rais]

I dont think there will be any bandwidth realated overheads, other than the additional header-fields/octets (24B) required by GRE to encapsulate the payload.

Other overheads may arise from fragmentation of origianl packets which could result in high CPU usage etc.

Thanks.