3Com S7906E Configuration Manual page 653

For OSPF TE configuration, refer to MPLS TE Configuration in the MPLS Volume.
IGP Shortcut and Forwarding Adjacency
IGP Shortcut and Forwarding Adjacency enable OSPF to use an LSP as the outbound interface for a
destination. Without them, OSPF cannot use the LSP as the outbound interface.
Differences between IGP Shortcut and Forwarding Adjacency:
If Forwarding Adjacency is enabled only, OSPF can also use an LSP as the outbound interface for
a destination
If LGP Shortcut is enabled only, only the router enabled with it can use LSPs for routing.
For configuration of this feature, refer to MPLS TE Configuration in the MPLS Volume.
VPN
OSPF supports multi-instance, which can run on PEs in VPN networks.
In BGP MPLS VPN networks, multiple sites in the same VPN can use OSPF as the internal routing
protocol, but they are treated as different ASs. An OSPF route learned by a site will be forwarded to
another site as an external route, which leads to heavy OSPF routing traffic and management issues.
Configuring area IDs on PEs can differentiate VPNs. Sites in the same VPN are considered as directly
connected. PE routers then exchange OSPF routing information like on a dedicated line; thus network
management and OSPF operation efficiency are improved.
For configuration of this feature, refer to MPLS L3VPN Configuration in the MPLS Volume.
OSPF sham link
An OSPF sham link is a point-to-point link between two PE routers on the MPLS VPN backbone.
In general, BGP peers exchange routing information on the MPLS VPN backbone using the BGP
extended community attribute. OSPF running on a PE at the other end utilizes this information to
originate a Type-3 summary LSA as an inter-area route between the PE and CE.
1-20