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CEF switching of unicast IP traffic on Supervisor 2, PFC2 and MSFC2 fails

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Wed, 07/22/2009 - 19:48
Jun 22nd, 2009
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Core Issue

Layer 3 (L3) switching is supported on the Supervisor 2, Policy Feature Card 2 (PFC2), and Multilayer Switch Feature Card 2 (MSFC2) as a Cisco Express Forwarding (CEF) enhancement called CEF for PFC2. This works with Protocol Independent Multicast (PIM) for switching multicast traffic (IP traffic only), and with CEF for switching unicast traffic (IP and Internetwork Packet Exchange (IPX) traffic only). It is enabled by default and cannot be disabled.

CEF switching of unicast IP traffic on the Supervisor 2, PFC2, and MSFC2 may fail due to routes not being present in the routing table, presence of incorrect information in the CEF tables on the MSFC2, or mismatches in the information in the CEF tables on the MSFC2 and PFC2.


Resolution

The CEF tables on the PFC2 mirrors the information in the CEF tables on the MSFC2. In turn, the CEF tables of the MSFC depends on the contents of the MSFC's routing table and successful Address Resolution Protocol (ARP) resolution of the next-hop addresses.

To resolve this issue, perform these steps:

  1. Verify that the information in the routing table and the ARP cache on the MSFC2 are accurate. Routes should be learned and installed in the routing table with the correct next-hop address, which should be resolved to the correct next-hop MAC address. To display the current state of the routing table, issue the show ip route command from user EXEC or privileged EXEC mode. To display the ARP cache, issue the show ip arp command from user EXEC or privileged EXEC mode.   
  2. Verify that the CEF tables on the MSFC2 contain the correct information. The Forwarding Information Base (FIB) table mirrors the information contained in the IP routing table. The next-hop address in the FIB table and the resolved next-hop information in the adjacency table must match the information in the routing table and the ARP cache. To display entries in the FIB, issue the show ip cef command from the user EXEC or privileged EXEC mode. To display the CEF adjacency table information, issue the show adjacency command from user EXEC or privileged EXEC mode.   
  3. Verify the information in the CEF tables on the PFC2, if the information in the routing table, ARP cache, and CEF tables on the MSFC2 are accurate. The information in the CEF tables on PFC2 must match the CEF tables on the MSFC2. To display CEF and adjacency entries on the PFC2, issue the show mls entry cef command.   

To resolve issues about CEF for PFC2, refer to How-To Troubleshoot Unicast IP Routing CEF on Catalyst 6000s with a Supervisor 2 in Hybrid Mode.

Catalyst 6000 systems with Supervisor 2 and MSFC2 running Catalyst OS (CatOS) versions 6.3(8), 6.3(9), or 7.3(2) may experience inconsistencies between the FIB tables on the Supervisor 2 and the MSFC2. For more information, refer to Field Notice: Inconsistency Between OS CEF Adjacency Table and Hardware CEF Adjacency Table in CatOS.

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