[c-nsp] high CPU utilization and GRE tunnels on Cisco 2800 series ISR

[Martin T]

Hi,

I have a Cisco 2811(IOS 12.4(11)XW7) router which has high(60 - 100%)
CPU utilization because of "IP Input"(takes care of IP packets which
are process-switched) process. CPU utilization has a clear correlation
with amount of packets processed. While this router has CEF
enabled("ip cef" in global configuration mode) it still shows that
almost all the traffic is process-switched according to "show
interfaces switching". At first I thought that this is probably
because of broadcast traffic or traffic addressed to the router, but I
excluded this after analyzing the output of "sh interfaces" and
debugging IP packets. In order to understand the top transit-traffic
destinations I configured NetFlow to both Fa0/0 and Fa0/1 and by far
the most packets are sent between three IP pairs which are all related
to GRE tunnels configured to this router. Destination addresses of
those three IP pairs are all in the CEF table. Still, is it possible
that GRE traffic in IOS is process-switched? As far as I know, it
should not be process switched. Tunnel configuration can be seen
below:

interface Tunnel0
 bandwidth 10000
 ip unnumbered FastEthernet0/0
 tunnel source FastEthernet0/1
 tunnel destination 10.10.10.195
 tunnel key 10213
 tunnel checksum
 tunnel path-mtu-discovery
end

Ass five(Tu0 - Tu5) GRE tunnels configured to this router have similar
configuration with exception that some have "ip mtu" or "keepalive"
configured.

Has anyone seen similar behavior before?


thanks,
Martin