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Cisco fast switching configured on interface but not working

Posted on 2010-09-14
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Last Modified: 2012-05-10
We have a router which was working fine until we changed the BGP configuration at which point it has a few memory fragmentation errors and the CPU utilisation shot up.
We backed out the changes to the BGP and even removed one of the peers and gave it a reboot but the high CPU persists. I have compared the running config against a backup and it is identicaly apart from the BGP peer that was removed.

I have tracked down the high CPU to the IP Input process and found that IP fast switching is disabled although it is enabled in the configuration.

interface GigabitEthernet0/0/0
 ip address xxx.xxx.170.202 255.255.255.248
 no ip redirects
 no ip proxy-arp
 ip route-cache policy
 negotiation auto
 no cdp enable
 no mop enabled

#show ip int gi0/0/0  

GigabitEthernet0/0/0 is up, line protocol is up

  Internet address is xxx.xxx.170.202/29

  Broadcast address is 255.255.255.255

  Address determined by configuration file

  MTU is 1500 bytes

  Helper address is not set

  Directed broadcast forwarding is disabled

  Multicast reserved groups joined: 224.0.0.5 224.0.0.6

  Outgoing access list is not set

  Inbound  access list is not set

  Proxy ARP is disabled

  Local Proxy ARP is disabled

  Security level is default

  Split horizon is enabled

  ICMP redirects are never sent

  ICMP unreachables are always sent

  ICMP mask replies are never sent

  IP fast switching is disabled

  IP fast switching on the same interface is disabled

  IP Flow switching is disabled

  IP CEF switching is disabled

  IP Null turbo vector

  IP multicast fast switching is enabled

  IP multicast distributed fast switching is disabled

  IP route-cache flags are Fast, Policy

  Router Discovery is disabled

  IP output packet accounting is disabled

  IP access violation accounting is disabled

  TCP/IP header compression is disabled

  RTP/IP header compression is disabled

  Policy routing is disabled

  Network address translation is disabled

  BGP Policy Mapping is disabled

  Input features: MCI Check

  WCCP Redirect outbound is disabled

  WCCP Redirect inbound is disabled

  WCCP Redirect exclude is disabled

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Question by:grblades
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joseleonardo earned 500 total points
ID: 33674136
Apply IP CEF in Global configuration...
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by:grblades
ID: 33674280
It was in the global configuration but wasnt active. A quick hunt through the logs and I found that in amongst the memory errors with the bigger BGP tables was one saying CEF was being disabled.
Re-entered the command and the cpu has dropped back down.

Thanks
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by:joseleonardo
ID: 33674650
Your Welcome!!!
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