H3C Technologies H3C SR8800 - Manual (Page 93)

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Before restart, the GR Restarter negotiates GR capability with GR Helpers. During the restart of the GR
Restarter, GR Helpers still advertise their adjacencies with the GR Restarter. After restart, the GR Restarter
sends GR Helpers an OSPF GR signal so that the GR Helpers do not reset their neighbor relationships
with the GR Restarter. Upon receiving responses from neighbors, the GR Restarter creates the neighbor
relationships.
After that, the GR Restarter synchronizes the LSDB with GR-capable neighbors, updates its routing table
and forwarding table, and removes stale routes.
TE and DS-TE
OSPF Traffic Engineering (TE) provides for the establishment and maintenance of Label Switched Paths
(LSPs) of TE.
When establishing Constraint-based Routed LSPs (CR LSPs), MPLS obtains the TE information of links in
the area via OSPF.
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.
NOTE:
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 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.
NOTE:
For configuration of this feature, see MPLS Configuration Guide.
VPN support
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 is forwarded to another site as an
external route. Thie mechanism 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 exchange OSPF routing information like on a dedicated line. Thus
network management and OSPF operation efficiency are improved.
NOTE:
For configuration of this feature, see MPLS Configuration Guide.