Inter-As Option C; Figure 79: Topology For Three-Label Stack Configuration For Inter-As Option - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BGP AND MPLS CONFIGURATION GUIDE 2010-10-12 Configuration Manual

JunosE 11.3.x BGP and MPLS Configuration Guide

Inter-AS Option C

Figure 79: Topology for Three-label Stack Configuration for Inter-AS Option C
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The labels that are generated to be sent to the inter-AS BGP peers are generated for
each next-hop PE router/received label tuple. Scaling is improved when all routes
advertised from a given VRF have the same label; this is the default E Series router
behavior. You can disable this behavior by issuing the ip mpls forwarding-mode
label-switched command for the VRF.
The third method of configuring inter-AS services and inter-AS VPNs is known as inter-AS
option C or 2547bis option C. This method is described in RFC 4364—BGP/MPLS IP Virtual
Private Networks (VPNs) (February 2006).
Inter-AS option C, similarly to the carrier-of-carriers configuration, requires a
label-switched path from a packet's ingress PE router to its egress PE router. Option C
introduces multihop EBGP redistribution of labeled VPN-IPv4 routes between source
and destination autonomous systems. Labeled IPv4 routes are redistributed by EBGP
between neighboring autonomous systems. Inter-AS option C uses BGP as the label
distribution protocol.
In an inter-AS option C network, ASBRs do not maintain or distribute VPN-IPv4 routes.
Each ASBR maintains labeled IPv4 /32 routes to the PE routers within its AS. The ASBR
distributes these routes to other autonomous systems with EBGP. If transit autonomous
systems are included in the topology, their ASBRs must also distribute the labeled /32
routes with EBGP. This configuration creates a label-switched path from the ingress PE
router to the egress PE router. This configuration enables the PE routers in different
autonomous systems to establish multihop EBGP connections to each other, and to
exchange VPN-IPv4 routes over those connections.
Two different configuration scenarios are possible with option C, one employing a
two-label stack and the other a three-label stack.
Figure 79 on page 408 illustrates the three-label stack scenario. PHP is not used in this
example.
Copyright © 2010, Juniper Networks, Inc.