H3C Technologies H3C S12500 Series Switches - Manual (Page 89)

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OSPF has a new LSA, Opaque LSA, which can be used for carrying TE information.
DiffServ Aware TE (DS-TE) provides for network resource optimization and allocation, flow classification,
and indication of network bandwidth consumption of each flow in a link. TE is implemented on the
classified type (thin granularity summarization type) rather than the summarized type (thick granularity
summarization type) to improve performance and bandwidth utilization.
To support DS-TE application in MPLS, OSPF supports Local Overbooking Multiplier TLV and Bandwidth
Constraint (BC) TLV.
For OSPF TE configuration, see MPLS Configuration Guide.
IGP shortcut and forwarding adjacency
IGP shortcut and forwarding adjacency enable OSPF to use an LSP as the output interface for a
destination. Without them, OSPF cannot use the LSP as the output interface.
Differences between IGP shortcut and forwarding adjacency:
• If forwarding adjacency is enabled only, OSPF can also use an LSP as the output interface for a
destination
• If IGP shortcut is enabled only, only the router enabled with it can use LSPs for routing.
For configuration of this feature, see MPLS Configuration Guide.
VPN support
OSPF supports VPN, which can run on PEs in VPN networks.
In BGP MPLS VPNs, 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.
To solve this problem, domain IDs are used to differentiate VPNs. Sites in the same VPN are considered
as directly connected. PE routers can exchange OSPF routing information like on a dedicated line, so
network management and OSPF operation efficiency are improved.
For configuration of this feature, see MPLS Configuration Guide.
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 by using the BGP
extended community attributes. OSPF running on the remote PE uses the routing information to originate
Type-3 summary LSAs (inter-area routes) transmitted to CEs.
If a CE has an intra-area route (backdoor route) to another CE, VPN traffic will always travel on the
backdoor route rather than the corresponding inter-area route because an intra-area route has a higher
priority than an inter-area route. To avoid this, establish an OSPF sham link between PEs to connect the
CEs through an intra-area route over the backbone area. For more information about sham link, see
MPLS Configuration Guide.
BFD Bidirectional forwarding detection (BFD) provides a single mechanism to quickly detect and monitor
the connectivity of links between OSPF neighbors, thus reducing network convergence time. For more
information about BFD, see High Availability Configuration Guide.
Protocols and standards
• RFC 1765, OSPF Database Overflow