Information Technology Reference
In-Depth Information
An outbound route map, To_asbr2, is used to permit only PE1 and RR1 addresses. Addi-
tionally, labels are permitted by the
set mpls-label
clause. In the opposite direction, only
addresses of RR2 and PE2 with labels are permitted into AS 100. These addresses are sub-
sequently redistributed into the local OSPF process, thus connecting the LSPs in two auton-
omous systems. Similar configurations are used in AS 200 (not shown).
Example 10-27 shows the label stack for the VPN prefix 172.16.0.0/16 on PE2. The next
hop is PE1 (192.168.100.2) for BGP and RR2 (192.168.47.7) for IGP. The VPN label 23,
Lv, is as advertised by PE1.
Example 10-27
Label Stack on PE2
PE2#show ip cef vrf VPNa 172.16.0.0
172.16.0.0/16, version 22, epoch 0, cached adjacency 192.168.47.7
0 packets, 0 bytes
tag information set
local tag: VPN-route-head
fast tag rewrite with Et1/0, 192.168.47.7, tags imposed: {19 23}
via 192.168.100.2, 0 dependencies, recursive
next hop 192.168.47.7, Ethernet1/0 via 192.168.100.2/32
valid cached adjacency
tag rewrite with Et1/0, 192.168.47.7, tags imposed: {19 23}
To reach PE1, PE2 uses an IGP label of 19 (L5). This label is replaced by 22 (L4) on RR2.
On ASBR2, a BGP route is used to reach PE1. The outgoing BGP label is 19 (L3), as shown
in Example 10-28. Note that the local BGP label 22 is passed on to LDP so that RR2 can
have the correct IGP label.
Example 10-28
BGP Label to Reach PE1 on ASBR2
ASBR2#show ip bgp label
Network Next Hop In Label/Out Label
192.168.100.2/32 192.168.56.5 22/19
192.168.100.3/32 192.168.56.5 23/20
192.168.100.4/32 192.168.67.7 20/nolabel
192.168.100.7/32 192.168.67.7 21/nolabel
The LFIB on ASBR2 is shown in Example 10-29. Note that the BGP labels are installed for
192.168.100.2 (PE1).
Example 10-29
LFIB on ASBR2
ASBR2#show tag forwarding
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
18 Pop tag 192.168.56.5/32 0 Et1/0 192.168.56.5
19 Pop tag 192.168.47.0/24 0 Et0/0 192.168.67.7
