Information Technology Reference
In-Depth Information
Figure 10-27
Prefix and Label Distribution for CSC
172.16.0.0/16
NH=ASBR2
192.168.100.4/32
NH=CE1
IGP Label=L5
192.168.100.4/32
NH=ASBR2
IGP Label=L1
ASBR2
ASBR1
AS 100
VPNa
Site1
AS 100
VPNa
Site2
CE1
AS 200
Backbone Carrier
CE2
192.168.100.4/32
NH=PE1
IGP Label=L4
192.168.100.4/32
NH=CE2
IGP Label=L2
PE1
PE2
200:1:192.168.100.4/32
BGP NH=PE2 RT=200:1
VPN Label=Lv
Backbone Carrier
172.16.0.0/16
NH=ASBR1
172.16.0.0/16
NH=ASBR4
AS 300
Enterprise
Customer
AS 400
Upstream
ISP
192.168.100.10/32
IGP NH=PE2
IGP Label=L3
ASBR3
ASBR4
Because LDP is enabled, ASBR2 advertises an IGP label, L1, for its loopback address
(192.168.100.4). The prefix is advertised by CE2 to PE2 in the common IGP between them.
Additionally, CE2 advertises an IGP label using LDP, L2, to PE2. The example of using
eBGP with labels between a PE and a CE is presented in the next section.
As the prefix 192.168.100.4/32 (ASBR2) from VPNa is redistributed into BGP on PE2, a
VPN label, Lv, is advertised from PE2 to PE1. Additionally, PE2 advertises an IGP label,
L3, for itself (192.168.100.10). After the VPNv4 prefix 200:1:192.168.100.4/32 is redis-
tributed into a VRF for VPNa, PE1 advertises the prefix 192.168.100.4/32 to CE1. Addi-
tionally, an IGP label, L4, is advertised. In turn, CE1 advertises L5 to ASBR1. Now ASBR1
has an LSP to ASBR2. ASBR1's loopback address (192.168.100.2) is advertised the same
way to ASBR2 (not shown).
Example 10-34 shows the LFIB on PE2, where 192.168.100.4 is ASBR2's loopback address
and 192.168.106.6 is CE2. Label 31 is the local VPN label for 192.168.100.4 advertised to
PE1 (Lv). Label 18 is a per-VRF IGP label received from CE2 (L2).
Example 10-34
LFIB on PE2
PE2#show tag forwarding
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
16 Pop tag 192.168.106.6/32 0 Et1/0 192.168.106.6
17 18 192.168.59.0/24[V] \
0 Et0/0 192.168.109.9
18 Pop tag 192.168.100.9/32 0 Et0/0 192.168.109.9
19 Aggregate 192.168.106.0/24[V] \
0
continues
