Route Redistribution For Ospf - Cisco NCS 6000 Series Configuration Manual

Route Redistribution for OSPF

prefix-set ospf-medium-prefixes
0.0.0.0/0 ge 32
end-set
Route Redistribution for OSPF
Redistribution allows different routing protocols to exchange routing information. This technique can be used
to allow connectivity to span multiple routing protocols. It is important to remember that the redistribute
command controls redistribution into an OSPF process and not from OSPF. See
Implementing OSPF , on page 334
OSPF Shortest Path First Throttling
OSPF SPF throttling makes it possible to configure SPF scheduling in millisecond intervals and to potentially
delay SPF calculations during network instability. SPF is scheduled to calculate the Shortest Path Tree (SPT)
when there is a change in topology. One SPF run may include multiple topology change events.
The interval at which the SPF calculations occur is chosen dynamically and based on the frequency of topology
changes in the network. The chosen interval is within the boundary of the user-specified value ranges. If
network topology is unstable, SPF throttling calculates SPF scheduling intervals to be longer until topology
becomes stable.
SPF calculations occur at the interval set by the timers throttle spf command. The wait interval indicates the
amount of time to wait until the next SPF calculation occurs. Each wait interval after that calculation is twice
as long as the previous interval until the interval reaches the maximum wait time specified.
The SPF timing can be better explained using an example. In this example, the start interval is set at
5 milliseconds (ms), initial wait interval at 1000 ms, and maximum wait time at 90,000 ms.
timers spf 5 1000 90000
Figure 17: SPF Calculation Intervals Set by the timers spf Command
This figure shows the intervals at which the SPF calculations occur as long as at least one topology change
event is received in a given wait interval.
Routing Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
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• Unmatched prefixes, including /32s, are placed in a low-priority queue.
Use the [no] spf prefix-priority route-policy rpl command to prioritize OSPF prefix installation into
the global RIB during SPF.
SPF prefix prioritization is disabled by default. In disabled mode, /32 prefixes are installed into the global
RIB, before other prefixes. If SPF prioritization is enabled, routes are matched against the route-policy
criteria and are assigned to the appropriate priority queue based on the SPF priority set. Unmatched
prefixes, including /32s, are placed in the low-priority queue.
If all /32s are desired in the high-priority queue or medium-priority queue, configure this single route
map:
for an example of route redistribution for OSPF.
Implementing OSPF
Configuration Examples for