3Com 3C13636 Configuration Manual page 877

Router 3000 ethernet family

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3Com Router 3000 Ethernet Family

Configuration Guide

Figure 3-10 Network diagram for advertising labeled VPN-IPv4 routes through

MP-EBGP between ASBRs

In terms of extensibility, advertising labeled VPN-IPv4 routes through MP-EBGP is prior

to managing VPN between ASBRs through subinterfaces.

When adopting MP-EBGP method, note that:

ASBRs perform no VPN-Target filtering on VPN-IPv4 routes that they receive from

each other. So the ISPs in different ASs that exchange VPN-IPv4 routes need to

reach a trust agreement on the route exchange.

VPN-IPv4 routes are exchanged only between VPN peers. A VPN user cannot

exchange VPN-IPv4 routes with the public network or with MP-EBGP peers with

whom it has not signed a trust agreement.

III. Advertising Labeled VPN-IPv4 Routes Through Multihop MP-EBGP

The two methods above require ASBRs to participate in maintaining and distributing

VPN-IPv4 routes. When all ASs need to exchange a great amount of VPN routes,

ASBRs may become the bottleneck that prevents the extension of network.

One solution is to make PEs exchange VPN-IPv4 routes directly with each other,

without the participation of ASBRs.

Two ASBRs advertise labeled IPv4 routes to PEs in their respective ASs through

ASBRs neither keep VPN-IPv4 routes nor advertise VPN-IPv4 routes in between.

ASBRs keep the labeled IPv4 routes of PEs in the AS and advertise them to the peers

in other ASs. The ASBR in the transit AS also advertises labeled IPv4 routes. Therefore,

an LSP is established between ingress PE and egress PE.

BGP/MPLS backbone

3Com Corporation

Chapter 3 BGP/MPLS VPN Configuration

BGP/MPLS backbone

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3c13636-us - router 3036 3000 series