Cisco Cisco IOS Software Release 12.0(23)S
MPLS VPN—Inter-AS—IPv4 BGP Label Distribution
Feature Overview
2
Cisco IOS Release 12.0(23)S
Feature Overview
This feature enables you to set up a VPN service provider network to exchange IPv4 routes with MPLS
labels. You can configure the VPN service provider network as follows:
labels. You can configure the VPN service provider network as follows:
•
Route reflectors exchange VPNv4 routes, using multihop, multiprotocol EBGP. This configuration
also preserves the next hop information and the VPN labels across the autonomous systems.
also preserves the next hop information and the VPN labels across the autonomous systems.
•
A local PE router (for example, PE1 in
) needs to know the routes and label information for
the remote PE router (PE2). This information can be exchanged between the PE routers and ASBRs
in one of two ways:
in one of two ways:
–
Internal Gateway Protocol (IGP) and Label Distribution Protocol (LDP): The ASBR can
redistribute the IPv4 routes and MPLS labels it learned from EBGP into IGP and LDP and vice
versa.
redistribute the IPv4 routes and MPLS labels it learned from EBGP into IGP and LDP and vice
versa.
–
Internal Border Gateway Protocol (IBGP) IPv4 label distribution: The ASBR and PE router
can use direct IBGP sessions to exchange VPNv4 and IPv4 routes and MPLS labels.
can use direct IBGP sessions to exchange VPNv4 and IPv4 routes and MPLS labels.
Alternatively, the route reflector can reflect the IPv4 routes and MPLS labels learned from the
ASBR to the PE routers in the VPN. This is accomplished by enabling the ASBR to exchange
IPv4 routes and MPLS labels with the route reflector. The route reflector also reflects the
VPNv4 routes to the PE routers in the VPN (as mentioned in the first bullet). For example, in
VPN1, RR1 reflects to PE1 the VPNv4 routes it learned and IPv4 routes and MPLS labels
learned from ASBR1. Using the route reflectors to store the VPNv4 routes and forward them
through the PE routers and ASBRs allows for a scalable configuration.
ASBR to the PE routers in the VPN. This is accomplished by enabling the ASBR to exchange
IPv4 routes and MPLS labels with the route reflector. The route reflector also reflects the
VPNv4 routes to the PE routers in the VPN (as mentioned in the first bullet). For example, in
VPN1, RR1 reflects to PE1 the VPNv4 routes it learned and IPv4 routes and MPLS labels
learned from ASBR1. Using the route reflectors to store the VPNv4 routes and forward them
through the PE routers and ASBRs allows for a scalable configuration.
•
ASBRs exchange IPv4 routes and MPLS labels for the PE routers, using EBGP.
Figure 1
VPNs Using EBGP and IBGP to Distribute Routes and MPLS Labels
RR1
PE1
CE1
CE2
VPN1
VPN2
PE2
RR2
ASBR1
ASBR2
Multihop
Multiprotocol
VPNv4
BGP IPv4 routes
and label with
multipath support
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