Information Technology Reference
In-Depth Information
Figure 10-32
Topology and BGP Sessions
Multi-hop eBGP VPNv4
iBGP IPv4 +
Label
RR2
RR1
iBGP VPNv4
IPv4 + Label
iBGP VPNv4
ASBR
1
ASBR
2
eBGP IPv4 + Label
AS 100
PE2
AS 200
PE1
172.16.0.0/16
eBGP IPv4
172.16.0.0/16
eBGP IPv4
AS 65000
AS 65000
VPNa
Site 2
VPNa
Site 1
CE2
CE1
To have reachability between RRs and PEs, loopback addresses must be exchanged. AS 100
decides to use redistribution so that loopback addresses of RR2 and PE2 are redistributed
on ASBR1 into its OSPF. AS 200 wants to isolate its OSPF from routes from AS 100 and
decides to use iBGP. Loopback addresses of RR1 and PE1 are advertised in iBGP and in
labels to RR2, which is an RR for both IPv4 and VPNv4 addresses. Both autonomous
systems use LDP to distribute their IGP labels.
The BGP next hop for VPNv4 prefixes is not changed between the two VPNv4 RRs. Both
autonomous systems also coordinate their RT policies so that routes within the same VPN
are properly imported and exported. To simulate VPNv4 prefix advertisement and label
distribution, 172.16.0.0/16 is generated in CE1.
Example 10-47 shows the relevant configurations on PE1. Under VRF VPNa, the RT
import of 200:200 is for Inter-AS routes from AS 200. PE1 has two BGP sessions: one to
CE1 (192.168.12.1) and one to RR1 (192.168.100.3). AS Override is configured with CE1.
Example 10-47
Relevant Configurations on PE1
ip vrf VPNa
rd 100:100
route-target export 100:100
route-target import 100:100
route-target import 200:200
!
ip cef
mpls label protocol ldp
