Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 252)

because the first network has 16 ones bits (255.255.0.0) whereas the second network has only 8
ones bits (255.0.0.0).
• ‐ For the less specific network, use the networks address as the ID.
‐ For the more specific network, use the network’s broadcast address as the ID. The
broadcast address is the network address, with all ones bits in the host portion of the
address. For example, the broadcast address for network 10.0.0.0 255.255.0.0 is
10.0.255.255.
If this comparison results in a change to the ID of an LSA that has already been generated, the
router generates a new LSA to replace the previous one. For example, if the router has already
generated an LSA for network with ID 10.0.0.0 for network 10.0.0.0 255.255.255.0, the router must
generate a new LSA for the network, if the router needs to generate an LSA for network 10.0.0.0
255.255.0.0 or 10.0.0.0 255.0.0.0.
OSPF graceful restart
The OSPF Graceful Restart feature provides support for high-availability routing. With this feature
enabled, disruptions in forwarding are minimized and route flapping diminished to provide continuous
service during times when a router experiences a restart.
With OSPF graceful restart enabled, a restarting router sends special LSAs to its neighbors called
grace LSAs. These LSAs are sent to neighbors either before a planned OSPF restart or immediately
after an unplanned restart. The grace LSA specifies a grace period for the neighbors of the restarting
router to continue using the existing routes to and through the router after a restart. The restarting
router comes up, it continues to use its existing OSPF routes as if nothing has occurred. In the
background, the router re-acquires its neighbors prior to the restart and recalculates its OSPF routes
and replaces them with new routes as necessary. Once the grace period has passed, the adjacent
routers return to normal operation.
NOTE
By default, graceful restart is enabled.
NOTE
If a Brocade ICX 6650 device is configured for OSPF graceful restart and is intended to be used in
switch over, the OSPF dead-interval should be changed to 60 seconds on OSPF interfaces to ensure
that the graceful restart process succeeds without a timeout.
OSPF stub router advertisement
OSPFv2 stub router advertisement is an open standard based feature and it is specified in RFC 3137.
This feature provides a user with the ability to gracefully introduce and remove an OSPFv2 router from
the network by controlling when the data traffic can start and stop flowing through the router in case
where there are other OSPFv2 routers present on the network providing alternative paths for the
traffic. This feature does not work if there is no alternative for the traffic through other OSPFv2 routers.
The router can control the data traffic flowing through it by changing the cost of the paths passing
through the configured router. By setting the path cost high the traffic will be redirected to other
OSPFv2 routers providing a lower cost path. This change in path cost is accomplished by setting the
metric of the links advertised in the Router LSA to a maximum value. When the OSPFv2 router is
ready to forward the traffic the links are advertised with the real metric value instead of the maximum
value.
OSPF graceful restart
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