Information Technology Reference
In-Depth Information
Example 10-23
LFIB on ASBR1 (Continued)
19 Pop tag 192.168.100.3/32 0 Et0/0 192.168.35.3
24 Pop tag 192.168.56.6/32 2360 Et1/0 192.168.56.6
25 16 100:100:172.16.0.0/16 \
0 Et0/0 192.168.35.3
Figure 10-18 shows packet forwarding. A label stack of 2 is pushed on PE2. L1 is the IGP
label toward ASBR1, and Lv2 is the VPN label. Because of PHP, ASBR2 pops the IGP label.
On ASBR1, a label stack is swapped on, with the top label, L2, reaching PE1, and the
bottom label, Lv1, as the new VPN label.
Figure 10-18
Packet Forwarding in the Inter-AS VPN with the Next Hop Unchanged Inside AS 200
PE1
ASBR1
ASBR2
PE2
AS 100
AS 200
AS 65000
AS 65000
VPNa
Site 1
VPNa
Site 2
CE1
CE2
Next Hop Reset by next-hop-self
When the default BGP next hop is reset on the receiving ASBR with
next-hop-self
, the
receiving ASBR assigns the VPNv4 prefix with a label stack. At the bottom of the stack, a
new VPN label is created. The top label is the IGP label for PE devices within the AS to
reach the ASBR's own loopback address, as in the case of a typical PE device.
Figure 10-19 shows a scenario with
next-hop-self
set on the receiving ASBR. In contrast
to Figure 10-17, the next hop is changed to ASBR2 when the VPNv4 prefix is advertised to
PE2. Because of the next-hop change, a new VPN label Lv3 is created on ASBR2.
