Information Technology Reference
In-Depth Information
As a PE router, PE3 advertises the PE4 address with a VPN label, Lv2. Additionally, PE3
advertises an IGP label, L3, to reach itself (192.168.100.10). Example 10-36 shows the
BGP label information on PE2. Label 23 is Lv2.
Example 10-36
Label Information on PE2
PE2#show ip bgp vpnv4 all label
Network Next Hop In label/Out label
Route Distinguisher: 300:1 (VPNa)
192.168.23.0 192.168.59.5 21/16
192.168.35.0 192.168.59.5 22/imp-null
192.168.47.0 192.168.100.10 33/21
192.168.59.0 192.168.59.5 23/aggregate(VPNa)
192.168.67.0 192.168.100.10 32/22
192.168.100.2/32 192.168.59.5 24/17
192.168.100.3/32 192.168.59.5 25/18
192.168.100.4/32 192.168.100.10 31/23
192.168.100.5/32 192.168.59.5 26/imp-null
192.168.100.6/32 192.168.100.10 30/30
192.168.100.7/32 192.168.100.10 29/31
192.168.106.0 192.168.100.10 28/32
192.168.201.0 192.168.100.10 27/33
As another PE router within CSC, PE2 advertises a BGP label, L4, for PE4's address for
VPNb. In label 31 in Example 10-36 is L4.
With regards to the customer prefix 172.16.0.0/16, CE2 is a P router; therefore, there is no
need for CE2 to store any information for the customer prefix. CE2 only needs to maintain
information for LSRs within AS 100.
An IGP label, L5, is advertised from CE2 to PE1. This completes the LSP from PE1 to PE4.
The LSP from PE4 to PE1 is set up the same way (not shown). Example 10-37 shows the
label stack on PE1. Label 21 is an IGP label used to reach PE4 (192.168.100.4) via CE2,
whereas label 27 is Lv.
Example 10-37
Label Stack on PE1
PE1#show ip cef vrf VPNa 172.16.0.0
172.16.0.0/16, version 11, epoch 0, cached adjacency 192.168.23.3
0 packets, 0 bytes
tag information set
local tag: VPN-route-head
fast tag rewrite with Et1/0, 192.168.23.3, tags imposed: {21 27}
via 192.168.100.4, 0 dependencies, recursive
next hop 192.168.23.3, Ethernet1/0 via 192.168.100.4/32
valid cached adjacency
tag rewrite with Et1/0, 192.168.23.3, tags imposed: {21 27}
