I have a Catalyst 3550 and 3750 stack in two separate locations, with GRE tunnels configured on our WAN links. Both switches are experiencing fairly high (70+ percent) CPU utilization, and the majority of this utilization is from the IP Input process.
The output of the following is from the Catalyst 3750. CEF is enabled on all interfaces, but the output of a "sho cef int <tunnel>" shows:
Interface is marked as point to point interface
Interface is marked as tunnel interface
Packets switched to this interface on linecard are dropped to next slow path
Packets switched to this interface are dropped to the next slow path
A "show cef not-cef-switched" shows a large (54 million in two days) number of packets in the "unsupported" column. Features on the tunnel interface include keepalives, pim sparse-dense-mode, and an ip multicast boundary.
A "show ip interface <tunnel>" shows:
IP fast switching is disabled
IP fast switching on the same interface is disabled
IP Flow switching is disabled
IP CEF switching is enabled
IP Null turbo vector
IP multicast fast switching is enabled
IP multicast distributed fast switching is disabled
IP route-cache flags are Fast, CEF
A "show interface <tunnel> stats" shows all packets being process switched.
Why is CEF switching punting all the packets? Why is fast switching disabled on the interface even though the route-cache flags show it being turned on?
The current IOS version on the 3750 is 12.1(19)EA1c. In the course of troubleshooting this problem, I learned that this version has security advisories, so I will be upgrading it, but based on the release notes I don't think that upgrading to 12.1(19)EA1d will solve the process switching issues.
There is also a 12.2(20)SE1 release, but according to the "image compare" feature on the Feature Navigator, it lacks not only CEF support but even support for the StackWise feature! Perhaps I'm misinterpreting, but I take this to mean that this release doesn't support multiple 3750's stacked together, which is a dealbreaker for me.
Any help on these issues would be greatly appreciated.
