Information Technology Reference
In-Depth Information
Example 10-35
Label Binding Information on PE1 (Continued)
192.168.100.4/32, rev 40
local binding: label: 31
remote binding: lsr: 192.168.100.5:0, label: 23
192.168.100.5/32, rev 30
local binding: label: 26
remote binding: lsr: 192.168.100.5:0, label: imp-null
192.168.100.6/32, rev 38
local binding: label: 30
remote binding: lsr: 192.168.100.5:0, label: 24
192.168.100.7/32, rev 36
local binding: label: 29
remote binding: lsr: 192.168.100.5:0, label: 25
192.168.106.0/24, rev 17
local binding: label: 19
remote binding: lsr: 192.168.100.5:0, label: 20
To reach 172.16.0.0/16, ASBR1 recursively resolves for the next-hop address ASBR2.
ASBR1 pushes an IGP label, L5, to the packet. This labeled packet is eventually replaced
with a label stack, L3 and Lv, on PE1. The label stack is then replaced by L2 on PE2. With
more label swapping and popping, eventually an IPv4 packet is delivered to AS 400.
Hierarchical VPN
When the customer carrier also provides MPLS VPN services, the CSC model becomes a
hierarchical VPN, as shown in Figure 10-28. As before, AS 200 is a backbone VPN provid-
er, and AS 100 is a customer provider that has two sites connected via VPNb. Now AS 100
also provides VPN services, where VPNa connects two sites. As another way to exchange
labels between a customer carrier and a backbone carrier within VPNb, eBGP with
IPv4 labels is used in this example. Thus, no IGP or LDP is needed between AS 100 CE
devices and AS 200 PE devices. The example of using an IGP and LDP between a CE and
a PE was presented in the previous section.
Figure 10-29 shows the process of prefix and label distribution, where 172.16.0.0/16 sim-
ulates an internal prefix within VPNa. Within AS 100, the RD for VPNa is 100:1. The cus-
tomer prefix 172.16.0.0/16 is attached with an RT of 100:1. In AS 200, 200:1 is configured
as the RD for VPNb. An RT of 200:1 is attached to the prefix of 192.168.100.4, which is
PE4's loopback address.
