Cisco Express Forwarding for IPv6

Cisco Express Forwarding (CEF) is a Layer 3 switching technology designed for routers. It uses a method that optimizes route lookups to achieve very fast forwarding. CEF uses two tables to store the information needed for routing: the Forwarding Information Database (FIB) and the adjacency table.

NOTE

CEF is supported on routers 1700, 2600, 3600, 3700, 7100, 7200, 7400, 7500, 7600, and the Catalyst 6500 and 12000 series.


There are two CEF modes:

  • Central CEF— The route processor handles CEF and adjacency tables. This mode is supported on router series 1700 to 7500.

  • Distributed CEF (dCEF)— This mode is used on distributed hardware architectures such as the Cisco 7500 VIP and Cisco 12000 line cards. dCEF performs the express forwarding of packets between port adapters and uses interprocess communications (IPC) to synchronize the CEF FIB and adjacency tables between router processors and linecards. The dCEF mode is supported on router series 7500 and 12000(GSR).

CEFv6's behavior is the same as CEF for IPv4. CEFv6 has new configuration commands, and CEFv6 and CEF for IPv4 have some of the same commands. This section presents the new commands used to manage CEF for IPv6 networks.

Enabling CEFv6 on Cisco

CEFv6 is available on Cisco IOS Software 12.2(13)T and above and 12.2(9)S and above. dCEFv6 is available on Cisco IOS Software 12.0(21)ST1, 12.0(22)S and above for the Cisco 12000 series, and 12.2(13)T for the Cisco 7500 series.

The ipv6 cef command enables the central CEFv6 mode. However, before you enable CEFv6, you must enable IPv4 CEF using the ip cef command. Similarly, you must enable IPv4 dCEF using the ip cef distributed command before you enable dCEFv6 with the ipv6 cef distributed command.

show Commands for CEFv6

You can display IPv6 information related to CEFv6 using the show ipv6 cef and the show cef commands. Table 4-14 shows the options and parameters of the show ipv6 cef command.

Table 4-14. show ipv6 cef Command Parameters
Command ParameterDescription
cef ipv6-prefix [detail]Shows IPv6 CEF information for the given IPv6 prefix.
cef interface [detail]Shows all IPv6 prefixes using the interface specified.
cef adjacency adjacencyShows all IPv6 prefixes resolving through the specified adjacency.
cef non-recursive [detail]Shows nonrecursive prefixes.
cef summaryShows IPv6 CEF table summary information.
cef traffic prefix-lengthShows per-prefix length accounting statistics.
cef unresolvedShows unresolved prefixes.
cef dropShows a counter of IPv6 and IPv4 packets dropped.
cef interface [detail] [statistics] interfaceShows CEF interface status and configuration.
cef linecard [detail] [statistics] slotShows CEF information related to linecards.
cef not-cef-switchedShows counters of IPv6 and IPv4 packets passed on to the next switching layer.

debug Commands for CEFv6

You can debug CEFv6 using the debug ipv6 cef command. Its options and parameters are shown in Table 4-15.

Table 4-15. debug ipv6 cef Command Parameters
Command ParameterDescription
dropsEnables debugging of packets dropped by CEFv6 switching.
eventsEnables debugging of control plane events for CEFv6.
hashEnables debugging of load-balancing hash setup events for CEFv6.
receiveEnables debugging packets passed to IPv6 process-level switching.
tableEnables debugging of CEFv6 table modification events.

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