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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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