2010-04-04 14:21:36
Cisco Express Forwarding (CEF)
The two main components of CEF are the forwarding information base (FIB) and the adjacency table. IP routing table is maintained by a router’s control plane. CEF operates in the data plane.
sh ip cef
Shows layer 3 forwarding information. Version is the version of the table and epoch is the number of times the table has been rebuilt.
[code]
R1#sh ip cef 10.1.1.1
10.1.1.1/32, version 42, epoch 0, receive
[/code]
clear ip cef epoch
Here you can see that I rebuild the CEF table and increase the epoch count.
[code]
R1#sh ip cef 10.1.1.1
10.1.1.1/32, version 42, epoch 0, receive
R1#clear ip cef epoch
R1#sh ip cef 10.1.1.1
10.1.1.1/32, version 42, epoch 1, receive
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sh ip cef 10.0.0.0 255.0.0.0 longer-prefixes
Attached, obviously the subnet is attached to this router. Receive, the router listens on that subnet or address.
[code]
R1#sh ip cef 10.0.0.0 255.0.0.0 longer-prefixes
Prefix Next Hop Interface
10.1.1.0/30 attached Serial0/0/0.12
10.1.1.0/32 receive
10.1.1.1/32 receive
10.1.1.3/32 receive
10.1.1.4/30 10.1.1.2 Serial0/0/0.12
10.1.1.8/30 10.1.1.2 Serial0/0/0.12
10.1.4.4/30 10.1.1.2 Serial0/0/0.12
10.1.4.8/30 10.1.1.2 Serial0/0/0.12
10.2.1.0/24 10.1.1.2 Serial0/0/0.12
10.2.2.0/24 10.1.1.2 Serial0/0/0.12
10.2.4.12/30 10.1.1.2 Serial0/0/0.12
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sh adjacency
Verifies an adjacency exists for a connected host.
[code]
R1#sh adjacency
Protocol Interface Address
IP Serial0/0/0.12 point2point(19)
IPV6 Serial0/0/0.12 point2point(10)
IP Serial0/1/0.15 point2point(7)
[/code]
Troubleshooting Layer 2 to Layer 3 Mapping
sh ip arp — Shows the ARP cache of the router, by default stores them for four hours. IT is the MAC address to IP address mapping.
sh frame-relay map — Displays the Frame Relay DLCIs and their next hop ip address.
sh adjacency detail — Displays information from a router CEF adjacency table.
sh ip arp
[code]
R4#sh ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.1.4.10 207 0018.1825.2543 ARPA FastEthernet0/1
Internet 10.1.4.9 – 001b.d421.480b ARPA FastEthernet0/1
Internet 10.1.4.6 41 0012.d9a5.1542 ARPA FastEthernet0/0
Internet 10.1.4.5 – 001b.d421.480a ARPA FastEthernet0/0
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sh frame-relay map
[code]
R1#sh frame-relay map
Serial0/0/0.12 (up): point-to-point dlci, dlci 102(0x66,0x1860), broadcast
status defined, active
Serial0/1/0.15 (up): point-to-point dlci, dlci 105(0x69,0x1890), broadcast
status defined, active
[/code]
sh adjacency detail
[code]
R1#sh adjacency detail
Protocol Interface Address
IP Serial0/0/0.12 point2point(19)
25 packets, 1940 bytes
18610800
CEF expires: 00:02:35
refresh: 00:00:35
Epoch: 0
IPV6 Serial0/0/0.12 point2point(10)
0 packets, 0 bytes
186186DD
IPv6 CEF never
Epoch: 0
IP Serial0/1/0.15 point2point(7)
32 packets, 3955 bytes
18910800
CEF expires: 00:02:26
refresh: 00:00:26
Epoch: 0
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