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To avoid unnecessary SPF calculation, when a router restarts, it will inform neighboring routers the
shutdown is temporary. Then these routers will not delete the router from their neighbor tables, and
other routers have no idea about this restart.
After recovering to normal, the router obtains the Link State Database from neighboring routers via the
GR related synchronization mechanism.
OSPF Graceful Restart
For GR information, refer to GR Overview in the High Availability Volume.
After an OSPF GR Restarter restarts, it needs to perform the following two tasks in order to
re-synchronize its LSDB with its neighbors.
z
To obtain once again effective OSPF neighbor information (assume the adjacencies are not
changed).
z
To obtain once again the LSDB.
After restart, the GR Restarter negotiates GR capability with its neighbors and sends an OSPF GR
signal to its GR-capable neighbors so that they will not remove their adjacencies with it and advertise
the adjacencies. The GR Restarter re-establishes neighborships and updates its own routing table and
forwarding table based on the new routing information received from neighbors and removes the stale
routes.
TE and DS-TETE
OSPF Traffic Engineering (TE) provides for the establishment and maintenance of Label Switch 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.