Multi-As Bgp/Mpls Vpn - 3Com 3C13636 Configuration Manual

3Com Router 3000 Ethernet Family
Configuration Guide
In some cases, the routes across the MPLS VPN backbone network need to be firstly
selected. You can establish a sham link between PEs to make the routes become the
Intra-Area Routes.
The sham link acts as an unnumbered point-to-point link inside the area and is
advertised using Type1 LSA. You can select a route between the sham link and
backdoor link by adjusting the metric.
The sham link is considered the link between two VPN instances with one endpoint
address in each VPN instance. The address is a Loopback interface address with a
32-bit mask in the VPN address space on the PE. The same OSPF process can share
endpoint addresses between sham links, while different OSPF processes cannot.
The BGP advertises the endpoint addresses of sham links as VPN-IPv4 addresses. A
route across the sham link cannot be redistributed into BGP as a VPN-IPv4 route.
The sham link can be configured in any area. You need to configure it manually in V
2.41. In addition, the local VPN instance must contain a route to the destination of sham
link.

3.1.6 Multi-AS BGP/MPLS VPN

In some networking scenarios, a user's multiple sites belong to the same VPN may
connect to multiple ISPs that use different ASs or connect to multiple ASs of an ISP.
Such application is called Multi-AS BGP/MPLS VPN.
RFC 2547bis presents three multi-AS VPN solutions, which are:
VPN-INSTANCE-to-VPN-INSTANCE: ASBRs manage VPN routes in between by
using subinterfaces, which is also called Inter-Provider Backbones Option A.
EBGP Redistribution of labeled VPN-IPv4 routes: ASBRs advertise labeled
VPN-IPv4 routes to each other through MP-EBGP, which is also called
Inter-Provider Backbones Option B.
Multihop EBGP redistribution of labeled VPN-IPv4 routes: PEs advertise labeled
VPN-IPv4 routes to each other through Multihop MP-EBGP, which is also called
Inter-Provider Backbones Option C.
The V 2.41 supports the above three solutions.
I. Managing VPN Routes Between ASBRs by Using Subinterfaces
PEs, acting as ASBRs in two ASs, are directly connected.
ASBR PEs connect to each other through multiple subinterfaces. Considering each
other as their CE, the ASBR PEs advertise IPv4 routes to the peer using traditional
EBGP. Each subinterface is associated with a VPN. You need to bind the subinterfaces
on the ASBR to their corresponding VPN-instances but do not need to enable MPLS on
them. Within an AS, packets are forwarded as VPN packets using two-tier labels;
between ASBRs, they are forwarded using IP routing.
Chapter 3 BGP/MPLS VPN Configuration
3Com Corporation
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