CEF Switching and the Adj table

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Guest

CEF Switching and the Adj table

Post by Guest » Tue Jan 11, 2011 3:36 pm


I have a 3750 stack of 4 switches.  There are multiple SVI interfaces on this switch.  I noticed that none of the physical interfaces report doing any CEF switching.  In fact all packets are reported as process switched.Example:SW3750G#sh int g1/0/1 statsGigabitEthernet1/0/1             Switch path    Pkts In   Chars In   Pkts Out  Chars Out               Processor          0          0    3497187  257226176             Route cache          0          0          0          0                   Total          0          0    3497187  257226176I do notice however that my SVI interfaces report a good portion of the packets to be CEF switched.Example:SW3750G#sh int vlan 1 stats  Vlan1             Switch path    Pkts In   Chars In   Pkts Out  Chars Out               Processor   48191591 3704212079   11627986 1243583236             Route cache      28845    3620783       4826    1718427                   Total   48220436 3707832862   11632812 1245301663It looks like CEF is not being used at all on any of the L2 interfaces.  I guess I always thought that CEF used the adjacency table when switching packets at L2.  Is CEF really only used when switching routed packets?

Guest

Re:CEF Switching and the Adj table

Post by Guest » Tue Jan 11, 2011 3:53 pm


IzackYes CEF is for layer 3 switching of packets. Therefore layer 2 interfaces do not use CEF to switch packets.HTHRick

Guest

Re:CEF Switching and the Adj table

Post by Guest » Tue Jan 11, 2011 4:32 pm


I guess the fact that switching on L2 interfaces is being reported as "process" switched was the thing that threw me off.  I know that L2 interfaces would typically use the mac address table to make switching decisions but just didn't understand why that would be reported in that way.  Thanks!

Guest

Re:CEF Switching and the Adj table

Post by Guest » Tue Jan 11, 2011 5:53 pm


Izack I was a bit surprised that it was reported this way (not what I would have expected). I also notice that it reports packets out and characters out but no packets in or characters in which seems unusual.I am glad that my response was able to resolve your question. Thank you for using the rating system to indicate that your question was resolved (and thanks for the rating). It makes the forum more useful when people can read a question and can know that there was a response which did resolve the question.The forum is an excellent place to learn about Cisco networking. I encourage you to continue your participation in the forum.HTHRick

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