12-06-2008 06:19 PM - edited 03-04-2019 12:37 AM
hi every body!
I read that routing table is copied into fib in CEF.
let say routing table has following entry
s 10.10.10.0 via 11.11.11.0
D 11.11.11.0 via 199.199.199.0 s0.
My question is if this entry is also present in fib, would switch cef- switch a packet destined to 10.10.10.1 or packet would be forwarded to layer 3 engine(essentiaaly router)?
thanks alot!
Solved! Go to Solution.
12-06-2008 09:57 PM
It will be CEF-Switched as well but it's a recursive route.
Rack1R4#sh run | i ip route
ip route 10.10.10.1 255.255.255.255 31.3.0.1
Rack1R4#sh ip route | i 31.3.0.0
R 31.3.0.0 [120/5] via 148.1.0.3, 00:00:00, Serial0/0.401
Rack1R4#sh ip cef 10.10.10.1
10.10.10.1/32, version 97, epoch 0, cached adjacency to Serial0/0.401
0 packets, 0 bytes
via 31.3.0.1, 0 dependencies, recursive
next hop 148.1.0.3, Serial0/0.401 via 31.3.0.0/16
Rack1R4#sh ip cef 31.3.0.1
31.3.0.0/16, version 31, epoch 0, cached adjacency to Serial0/0.401
0 packets, 0 bytes
via 148.1.0.3, Serial0/0.401, 0 dependencies
next hop 148.1.0.3, Serial0/0.401
valid cached adjacency
Excellent question, Sarah !
__
Edison.
12-06-2008 09:52 PM
The CEF FIB table is built with the help of routing table. It holds the next-hop information.
In addition CEF also builts a adjacency table which holds the necessary layer 2 information (encap, mac-address etc) which would be required for sending the packet using that route.
Hence when a packet arrives, the FIB is used to check the next-hop information and then using the adjacency table the L2 packet rewrite is performed and the packet is forwarded.
HTH
Narayan
Narayan
12-06-2008 09:57 PM
It will be CEF-Switched as well but it's a recursive route.
Rack1R4#sh run | i ip route
ip route 10.10.10.1 255.255.255.255 31.3.0.1
Rack1R4#sh ip route | i 31.3.0.0
R 31.3.0.0 [120/5] via 148.1.0.3, 00:00:00, Serial0/0.401
Rack1R4#sh ip cef 10.10.10.1
10.10.10.1/32, version 97, epoch 0, cached adjacency to Serial0/0.401
0 packets, 0 bytes
via 31.3.0.1, 0 dependencies, recursive
next hop 148.1.0.3, Serial0/0.401 via 31.3.0.0/16
Rack1R4#sh ip cef 31.3.0.1
31.3.0.0/16, version 31, epoch 0, cached adjacency to Serial0/0.401
0 packets, 0 bytes
via 148.1.0.3, Serial0/0.401, 0 dependencies
next hop 148.1.0.3, Serial0/0.401
valid cached adjacency
Excellent question, Sarah !
__
Edison.
12-07-2008 05:35 AM
Thanks alot Edison for your reply and kind remarks!
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