3Com 3C13636 Configuration Manual page 867

Router 3000 ethernet family

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3Com Router 3000 Ethernet Family

Configuration Guide

Routing information exchange between ingress PE and egress PE

The ingress PE router uses MP-BGP to advertise routing information learned from CE

to the egress PE router (with MPLS label) and learn the CE routing information learned

at the egress PE router.

The internal connectivity among all the PEs is ensured via IGP (for example, RIP and

OSPF), so IGP should run at all interconnection interfaces and loopback interfaces.

LSP setup between PEs

LSPs should be set up between PEs for VPN data traffic forwarding with MPLS LSP.

The PE router that receives packets from CE and create label protocol stack is called

ingress LSR, while the BGP next hop (egress PE router) is egress LSR.

Routing information exchange between PE and CE

A CE can learn remote VPN routes from the PE connected through static routes, RIP,

OSPF or EBGP.

With above-mentioned steps, reachable routes can be established between CEs, for

transmission of VPN private routing information over public network.

II. Forwarding VPN packets

VPN packets are forwarded by adopting two-layer label mode:

Interior-layer label, also called MPLS label, is at the bottom in label stack and

distributed when the egress PE advertises routing information (in VPN forwarding table)

to ingress GE. When VPN packets from public network reach the CE, they can be

forwarded from the designated interface to the designated CE or site by searching for

the target MPLS forwarding table according to the labels contained.

Exterior-layer label, known as LSP initialization label, is at the top in label stack and

indicates an LSP from the ingress PE to egress PE. By switching exterior-layer label,

VPN packets can be forwarded along the LSP to the peer PE.

Figure 3-3 illustrates the details:

Figure 3-3 VPN packet forwarding

3Com Corporation

Chapter 3 BGP/MPLS VPN Configuration

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3c13636-us - router 3036 3000 series