Brocade Multi-Service IronWare Routing Configuration Guide (Supporting R05.6.00) - Manual (Page 192)

164 Multi-Service IronWare Routing Configuration Guide
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OSPF graceful restart
Hitless upgrade support for OSPF graceful restart
OSPF graceful restart experiences minimal packet loss during hitless upgrade on a non-default
VRF. On a default VRF, there is no packet loss during hitless upgrade.
OSPF Stub Router Advertisement
OSPFv2 Stub Router Advertisement is an open standard based feature and it is specified in RFC
3137. This feature, introduced in version 03.2.00, 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.
The feature is useful for avoiding a loss of traffic during short periods when adjacency failures are
detected and traffic is rerouted. Using this feature, traffic can be rerouted before an adjacency
failure occurs due to common services interruptions such as a router being shutdown for
maintenance.
The feature is also useful during router startup because it gives the router enough time to build up
its routing table before forwarding traffic. This can be useful where BGP is enabled on the router
because it takes time for the BGP routing table to converge.
Version 03.5.00 of the Multi-Service IronWare software introduced an enhancement that allows
you to configure and set a metric value for the following LSA types:
• Summary (type 3 and type 4)
• External (type 5 and type 7)
• Opaque (type 10, TE link)
Configuration of this feature is described in “Configuring OSPF router advertisement” on page 211.
OSPF Shortest Path First throttling
Version 03.2.00 of the Multi-Service IronWare software introduced rapid triggering of SPF
calculations with exponential back-off to offer the advantages of rapid convergence without
sacrificing stability. As the delay increases, multiple topology changes can occur within a single
SPF. This dampens network activity due to frequent topology changes.
This scheduling method starts with an initial value after which a configured delay time is followed.
If a topology change event occurs the SPF is schedule after the time specified by the initial value,
the router starts a timer for the time period specified by a configured hold time value. If no topology
events occur during this hold time, the router returns to using the initial delay time.
If a topology event occurs during the hold time period, the next hold time period is recalculated to a
value that is double the initial value. If no topology events occur during this extended hold time, the
router resets to its initial value. If an event occurs during this extended hold time, the next hold time
is doubled again. The doubling occurs as long as topology events occur during the calculated hold