Cisco Cisco IOS Software Release 12.0(22)S
MPLS VPN—Inter-AS—IPv4 BGP Label Distribution
Feature Overview
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Cisco IOS Release 12.0(22)S
Using Route Maps to Filter Routes
When both routers are configured to distribute routes with MPLS labels, all the routes are encoded with
the multiprotocol extensions and contain an MPLS label. You can use a route map to control the
distribution of MPLS labels between routers. Route maps enable you to specify the following:
the multiprotocol extensions and contain an MPLS label. You can use a route map to control the
distribution of MPLS labels between routers. Route maps enable you to specify the following:
•
For a router distributing MPLS labels, you can specify which routes are distributed with an MPLS
label.
label.
•
For a router receiving MPLS labels, you can specify which routes are accepted and installed in the
BGP table.
BGP table.
Benefits
Using BGP to distribute IPv4 routes and MPLS labels routes has the following benefits:
Having the route reflectors store VPNv4 routes results in improved scalability
This configuration scales better than other configurations where the ASBR holds all of the VPNv4 routes
and forwards based on VPNv4 labels. With this configuration, route reflectors hold the VPNv4 routes,
which simplifies the configuration at the border of the network.
and forwards based on VPNv4 labels. With this configuration, route reflectors hold the VPNv4 routes,
which simplifies the configuration at the border of the network.
Enables a non-VPN core network to act as a transit network for VPN traffic
The configuration example illustrated in
shows that you can transport IPv4 routes with MPLS
labels over a non MPLS VPN service provider.
Eliminates the need for any other label distribution protocol between adjacent LSRs
If two adjacent label switch routers (LSRs) are also BGP peers, BGP can handle the distribution of the
MPLS labels. No other label distribution protocol is needed between the two LSRs.
MPLS labels. No other label distribution protocol is needed between the two LSRs.
Restrictions
This feature includes the following restrictions:
•
For networks configured with EBGP multihop, an LSP must be established between nonadjacent
routers. (RFC 3107)
routers. (RFC 3107)
•
This feature does not currently support multiple routes to a given destination.
•
The PE routers must run images that support BGP label distribution. Otherwise, you cannot run
EBGP between them.
EBGP between them.
•
This feature is not supported with eiBGP multipath.
•
The physical interfaces that connect the BGP speakers must support Cisco Express Forwarding
(CEF) or distributed CEF and MPLS.
(CEF) or distributed CEF and MPLS.