Huawei Quidway NetEngine80E Configuration Manual page 291

HUAWEI NetEngine80E/40E Router
Configuration Guide - IP Routing
IGP Shortcut and Forwarding Adjacency
OSPF TE supports either IGP shortcut aor Forwarding Adjacency (FA). This two features allow
OSPF TE to establish an LSP to reach a specified destination. Without the two features, OSPF
cannot use the LSP as an outgoing interface even if the LSP to the destination exists.
The differences between IGP Shortcut and forwarding adjacency are as follows:
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OSPF VPN Multi-instance
OSPF supports multi-instance, which can run between PEs and CEs in VPN networks.
In BGP MPLS VPN, many sites of one VPN can use OSPF as the internal routing protocol. The
sites, however, are handled as being from different ASs. In this way, the OSPF routes learned
on one site are transmitted as external routes to another site. This causes a heavy OSPF traffic
and some avoidable network management problems.
In the NE80E/40E implementation, you can configure domain IDs on a PE to differentiate the
VPNs where different sites reside. Different sites in one VPN consider each other as if they were
connected directly. Therefore, PEs exchange OSPF routing information as if they were directly
connected through a leased line. This improves network management and enhances the validity
of the OSPF application.
OSPF Sham Links
OSPF sham links are unnumbered P2P links between two PEs over an MPLS VPN backbone
network.
Generally, BGP extended community attributes carry routing information over the MPLS VPN
backbone between BGP peers. OSPF running on the remote PE uses this information to generate
Type3 summary LSAs from PE to CE. These routes are considered as inter-area routes.
If a router, however, connects to PEs in its own area and establishes an intra-area route to a
particular destination, the VPN traffic always traverses the route rather than the backbone route.
This is because OSPF intra-area routes in the routing table have relatively higher priorities. To
prevent this, an unnumbered P2P sham link is configured between the PEs. This provides an
intra-area path with a lower cost to the PE.
Issue 02 (2014-09-30)
If only forwarding adjacency is enabled, OSPF can reach the destination by using the LSP.
If only IGP Shortcut is enabled, only the router enabled with IGP Shortcut can use the LSP.
NOTE
For detailed configuration of this feature, refer to the HUAWEI NetEngine80E/40E Router Configuration
Guide - MPLS.
NOTE
For detailed configuration of this feature, refer to the HUAWEI NetEngine80E/40E Router Configuration
Guide - VPN.
NOTE
For configurations of OSPF sham links, refer to the HUAWEI NetEngine80E/40E Router Configuration
Guide - VPN.
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