GRE Tunnel

robert.horrigan · ‎02-14-2008

Howdy,

I have a large number of GRE tunnels in my org. Occasionally the tx rate maxes out. I understand that all data is encapsulated through the wan interface so my question is, what packets are transmited on the gre tunnel interface and why does it max out? I know it is only 9K so if all traffic goes through this tunnel then why is it always not maxed out?

Richard Burts · ‎02-14-2008

Robert

I am not sure that we have enough information at this point to answer the question of what packets are transmited on the gre tunnel interface. To answer that we would need to know what in the routing table points to the GRE tunnel as the path to get to certain destinations. And there might also be Policy Based Routing configured which could be sending traffic over the GRE but not show up in the IP routing table.

But part of the question we can answer. Since the GRE tunnel is a virtual interface its real capacity (bandwidth) is dependent on its outbound physical interface. The fact that the show interface indicates a bandwidth of 9 K reflects the fact that Cisco had to plug in some number. But the capacity of the tunnel is almost ceratinly greater than 9 K.

HTH

Rick

HTH

Rick

robert.horrigan · ‎02-14-2008

A static route forwards all traffic through that tunnel. Just seems odd that the tunnel would fluctuate from 1/255 to 255/255 tx rate when the wan interface it is using, a T3, is almost always at 50% during prime hours. Does the tx rate on the gre tunnel reflect the 9K or the T3 43K?

Richard Burts · ‎02-15-2008

Robert

The tx rate on an interface uses the bandwidth of that interface. So the tx rate on the tunnel will use the 9 K in its calculation. It certainly would not take much traffic through the tunnel to put it at 255/255. If you are going to look at tx rate and treat it as a reasonable number then I suggest that you configure the tunnel with a reasonable bandwidth that reflects your environment.

HTH

Rick

HTH

Rick