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

Martin T m4rtntns at gmail.com
Mon Dec 1 04:05:04 EST 2014


thanks! Once I disabled the checksum calculation for GRE header and
payload, the process switched traffic dropped from ~600 pps in both
directions on Fa0/0 and Fa0/1 to 7-8 pps. Rest of the traffic is
CEF-switched. CPU usage is around 10%.


On 11/28/14, Lukas Tribus <luky-37 at hotmail.com> wrote:
>> interface Tunnel0
>> bandwidth 10000
>> ip unnumbered FastEthernet0/0
>> tunnel source FastEthernet0/1
>> tunnel destination
>> 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?
> I strongly suggest to disable "tunnel checksum", because this will
> bypass CEF and you end up process switching everything (a part from
> the fact the the actual checksumming takes it toll as well).
> Regards,
> Lukas

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