Use of GRE Tunnel transmit and receive bandwidth

[Thiyagarajan K]

Hello All,

I'm troubleshooting the performance issue of traffic through the GRE tunnel between two sites. I have noticed the tunnel bandwidth and receive are set to 8 Mb as default.

- Does the default value of 8Mb mean the tunnel would rate limit the traffic to 8Mb?

- If I increase the tunnel bandwidth value to the bandwidth of the ISP link 100 Mb, will it improve the throughput of the traffic flow through the tunnel?

- what is the use of these commands? or why do we need these commands?

show int Tunnel120
Tunnel120 is up, line protocol is up

Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)

Thanks a lot in advance for your help.

Regards,

Thiyagu

[Richard Burts]

Thiyagu

To answer your question let us start with some basics:

- in Cisco configuration bandwidth is a descriptor which describes the capacity of the interface. It is a description and does not impact the actual operation of the interface. Note that bandwidth can be used as part of a configuration that does rate limiting or policing but in that case bandwidth does not change the operational characteristic but it is changed by the rate limiting or policing commands.

- on a physical interface there can be a clear basis for selecting the value used as bandwidth for that interface. But for virtual interfaces such as tunnel interfaces, how do you select an appropriate value for bandwidth since we have no way of knowing what are the operating characteristics as the tunnel traffic is sent through the exit interface. So Cisco adopts the very reasonable approach of setting the bandwidth of tunnel interfaces to a quite low value.

So unless there is some rate limiting or policing in the configuration then the tunnel bandwidth would not rate limit traffic going through the tunnel. And if you increase the tunnel bandwidth it should not improve the throughput of the traffic. I would be quite surprised if there turns out to be any relationship between the tunnel bandwidth and the performance problems that you are investigating.

HTH

Rick