Total neighbor count: 1
OSPF FIB Download Notification
OSPF FIB Download Notification feature minimizes the ingress traffic drop for a prolonged period of time
after the line card reloads and this feature is enabled by default.
Open Shortest Path First (OSPF) registers with Routing Information Base (RIB) through Interface Table
Attribute Library (ITAL) which keeps the interface down until all the routes are downloaded to Forwarding
Information Base (FIB). OSPF gets the Interface Up notification when all the routes on the reloaded line card
are downloaded through RIB/FIB.
RIB provides notification to registered clients when a:
•
Node is lost.
•
Node is created.
•
Node's FIB upload is completed.
Designated Router (DR) for OSPF
On point-to-point and point-to-multipoint networks, the Cisco IOS XR software floods routing updates to
immediate neighbors. No DR or backup DR (BDR) exists; all routing information is flooded to each router.
On broadcast or NBMA segments only, OSPF minimizes the amount of information being exchanged on a
segment by choosing one router to be a DR and one router to be a BDR. Thus, the routers on the segment
have a central point of contact for information exchange. Instead of each router exchanging routing updates
with every other router on the segment, each router exchanges information with the DR and BDR. The DR
and BDR relay the information to the other routers. On broadcast network segments the number of OSPF
packets is further reduced by the DR and BDR sending such OSPF updates to a multicast IP address that all
OSPF routers on the network segment are listening on.
The software looks at the priority of the routers on the segment to determine which routers are the DR and
BDR. The router with the highest priority is elected the DR. If there is a tie, then the router with the higher
router ID takes precedence. After the DR is elected, the BDR is elected the same way. A router with a router
priority set to zero is ineligible to become the DR or BDR.
Default Route for OSPF
Type 5 (ASE) LSAs are generated and flooded to all areas except stub areas. For the routers in a stub area to
be able to route packets to destinations outside the stub area, a default route is injected by the ABR attached
to the stub area.
The cost of the default route is 1 (default) or is determined by the value specified in the default-cost command.
Link-State Advertisement Types for OSPF Version 2
Each of the following LSA types has a different purpose:
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
417
Implementing OSPF
OSPF FIB Download Notification
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