Information Technology Reference
In-Depth Information
Figure 10-4 Interaction of FIB and LFIB
RIB
LIB
TE Tunnel
FIB
LFIB
Adjacency
Ta b l e
Label
Rewrite
CEF is the preferred switching mechanism for IP packets and is the only method that
supports MPLS. When MPLS is enabled, CEF also allows table lookup based on labels.
The label forwarding information is stored in LFIB. Example 10-7 shows a sample LFIB.
Example 10-7 Sample LFIB as Output of show mpls forwarding
R2#show mpls forwarding
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
16 Pop tag 192.168.45.0/24 0 Et2/0 192.168.24.4
17 17 192.168.56.0/24 0 Et2/0 192.168.24.4
19 192.168.56.0/24 0 Et1/0 192.168.23.3
18 Pop tag 192.168.35.0/24 0 Et1/0 192.168.23.3
19 Pop tag 192.168.100.4/32 711 Et2/0 192.168.24.4
20 20 192.168.100.5/32 0 Et2/0 192.168.24.4
21 192.168.100.5/32 0 Et1/0 192.168.23.3
21 21 192.168.100.6/32 0 Et2/0 192.168.24.4
22 192.168.100.6/32 0 Et1/0 192.168.23.3
22 Untagged 192.168.100.1/32 2360 Et0/0 192.168.12.1
23 Pop tag 192.168.100.3/32 1143 Et1/0 192.168.23.3
This example shows three forms of labels on the outgoing side: a label, label popping (Pop
tag), and no label (Untagged). If a label is indicated, label swapping is performed. If
“Pop tag” is shown, the top label must be popped before forwarding. If “Untagged” is
indicated, all labels are removed before forwarding.
For an outgoing label to be installed in the LFIB for prefix P , in addition to having a remote
binding from the next-hop neighbor for P , the next-hop IP address for the prefix (shown in
show ip route P or show ip cef P ) must also be in the set of addresses displayed for the
neighbor in show mpls ldp neighbor .
NOTE
 
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