Information Technology Reference
In-Depth Information
Figure 10-19
Inter-AS VPN with the
next-hop-self
Setting on the Receiving ASBR
100:100:172.16.0.0/16
NH=PE1, RT=100:1
VPNv4 Label=Lv1
100:100:172.16.0.0/16
NH=ASBR1, RT=100:1
VPNv4 Label=Lv2
100:100:172.16.0.0/16
NH=ASBR2, RT=100:1
VPNv4 Label=Lv3
PE2
PE1
ASBR1
ASBR2
AS 100
AS 200
172.16.0.0/16
NH=CE1
172.16.0.0/16
NH=PE2
AS 65000
AS 65000
VPNa
Site 1
VPNa
Site 2
CE1
CE2
Example 10-24 shows a sample LFIB on ASBR2. The VPNv4 prefix 100:100:172.16.0.0/16
is in the LFIB. The incoming label 23 is Lv3, because of PHP in AS 200. The outgoing label
25 is Lv2. The function of ASBR1 remains unchanged from the previous case.
Example 10-24
LFIB with the Next Hop Reset on ASBR2
ASBR2#show tag forwarding
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
16 Untagged 192.168.35.0/24 0 Et1/0 192.168.56.5
17 Untagged 192.168.100.5/32 0 Et1/0 192.168.56.5
18 Pop tag 192.168.47.0/24 0 Et0/0 192.168.67.7
19 16 192.168.100.4/32 0 Et0/0 192.168.67.7
20 Pop tag 192.168.100.7/32 0 Et0/0 192.168.67.7
21 Pop tag 192.168.56.5/32 7670 Et1/0 192.168.56.5
23 25 100:100:172.16.0.0/16 \
0 Et1/0 192.168.56.5
Multihop Multiprotocol eBGP for VPNv4
Route reflection was discussed in Chapter 7, “Scalable iBGP Design and Implementation
Guidelines,” as a way to scale the iBGP connectivity for IPv4. Route reflection can also
be used for VPNv4 for the same purpose. The use of route reflection to increase VPNv4
scalability is discussed in detail later in the section “Deployment Considerations.” This
section focuses on how route reflection is related to inter-AS VPN connectivity.
In an inter-AS VPN environment, route reflectors (RRs) might already maintain all the
VPNv4 information for the AS. Therefore, it is logical to exchange the inter-AS VPN
information directly between RRs, without burdening ASBRs. This reduces resource use
