Ospf Vpn Extension - 3Com 3C13636 Configuration Manual

3Com Router 3000 Ethernet Family
Configuration Guide
for the PE-CE downstream traffic, this function is implemented via static routing. The
static routing in a multi-role host application is different from the regular static routes in
the sense that it enables a logical interface to access multiple VPNs by making use of
the static route on a VPN to specify an interface in some other VPN as the outgoing
interface.

3.1.5 OSPF VPN Extension

I. OSPF multi-instance
As one of the most popular IGP routing protocols, OSPF is used as internal routing
protocol in many VPNs. If OSPF is also used on PE-CE links, then CE routers only
need to support OSPF protocol. If you want to transform conventional OSPF backbone
into BGP/MPLS VPN, the OSPF can simplify this process.
When OSPF is used as PE-CE routing protocol in BGP/MPLS VPN application,, PE
must support OSPF multi-instance, one OSPF instance corresponds to one VPN
instance. It owns its own interface, routing table and sends VPN routing information
over MPLS network using BGP/OSPF interaction.
The following involves details about the OSPF configuration between PE and CE.
1) OSPF domain configuration between PE and CE
The OSPF domain between PE and CE can be a non-backbone area or a backbone
area.
In the application of OSPF VPN extension, the MPLS VPN backbone network is
considered as the backbone area (area 0). All the areas should be connected with the
backbone area in OSPF, so area 0 of all the VPN nodes must be connected with the
MPLS VPN backbone network.
That is, if a VPN node involves OSPF domain 0, the PE connected to CE must connect
with the backbone area of the VPN node through area 0 (The virtual link can be used
for logical connection).
2) BGP/OSPF interaction
After OSPF runs between PE and CE, PE advertises VPN routes to other PEs through
BGP and to CEs through OSPF.
As shown in Figure 3-6, PE1 connects to PE2 through the MPLS backbone network.
CE11, CE21, and CE22 belong to VPN1. Suppose all the routers in the figure belong to
the same AS, that is, CE11, CE21, and CE22 belong to the same OSPF area.
The advertisement procedure of VPN1 routes is as follows:
BGP redistributes OSPF routes of CE11 on PE1.
BGP advertises the VPN routes to PE2.
OSPF redistributes BGP VPN routes on PE2, and advertises them to CE21 and
CE22.
Chapter 3 BGP/MPLS VPN Configuration
3Com Corporation
3-10