Information Technology Reference
In-Depth Information
When an IPv4 packet destined for 172.16.0.0/16 is received from CE1, PE1 pushes two
labels to the packet, L5 and Lv. Upon receiving such a packet, CE2 replaces L5 with L4.
As a CSC PE, PE2 accepts labeled packets for which it has assigned labels. Because the
labeled packet comes from VPNb, L4 is replaced with a label stack, L3 and Lv2. Now the
packet has three labels—L3, Lv2, and Lv.
Assuming the default PHP, PE3 receives the packet with Lv2 and Lv. As a PE enabled with
CSC, PE3 replaces the top label (Lv2) with L2. Example 10-38 shows the LFIB on PE3.
Label 23 is Lv2, and label 18 is the BGP label L2 advertised by CE3.
Example 10-38 LFIB on PE3
PE3#show tag forwarding
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
16 Pop tag 192.168.100.9/32 0 Et0/0 192.168.109.9
21 29 192.168.47.0/24[V] \
1298 Et1/0 192.168.106.6
22 32 192.168.67.0/24[V] \
0 Et1/0 192.168.106.6
23 18 192.168.100.4/32[V] \
16278 Et1/0 192.168.106.6
30 Pop tag 192.168.100.6/32[V] \
0 Et1/0 192.168.106.6
31 17 192.168.100.7/32[V] \
4295 Et1/0 192.168.106.6
32 Aggregate 192.168.106.0/24[V] \
1040
33 Pop tag 192.168.201.0/24[V] \
0 Et1/0 192.168.106.6
34 26 192.168.100.5/32[V] \
0 Et0/0 192.168.109.9
35 25 192.168.100.3/32[V] \
4685 Et0/0 192.168.109.9
36 24 192.168.100.2/32[V] \
10438 Et0/0 192.168.109.9
37 23 192.168.59.0/24[V] \
0 Et0/0 192.168.109.9
39 22 192.168.35.0/24[V] \
118 Et0/0 192.168.109.9
40 21 192.168.23.0/24[V] \
2360 Et0/0 192.168.109.9
At CE3, L2 is replaced with L1. Assuming the default PHP, PE4 receives the packet with
one label, Lv. An IPv4 packet is then delivered to CE4.
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