Open Shortest Path First (OSPFv2) | 361
Depending on the type, the link ID has different meanings.
• 1: point-to-point connection to another router neighboring router
• 2: connection to a transit network IP address of Designated Router
• 3: connection to a stub network IP network/subnet number
• 4: virtual link neighboring router ID
LSA Throttling
LSA throttling provides configurable interval timers to improve OSPF convergence times. The default
OSPF static timers (5 seconds for transmission, 1 second for acceptance) ensure sufficient time for sending
and resending LSAs and for system acceptance of arriving LSAs. However, some networks may require
reduced intervals for LSA transmission and acceptance. The throttling timers allow for this improved
convergence times.
Configure the LSA throttling timers in milliseconds, with the interval time increasing exponentially until a
maximum time has been reached. If the maximum time is reached, the system continues to transmit at the
max-interval until twice the max-interval time has passed. At that point, the system reverts to the
start-interval timer and the cycle begins again.
When you configure the LSA throttle timers, syslog messages appear, indicating the interval times
(Message 1) and (Message 2).
Message 1 SYSLOG message for LSA transmit timer (45000 msec in this example)
Mar 15 09:46:00: %STKUNIT0-M:CP %OSPF-4-LSA_BACKOFF: OSPF Process 10,Router lsa id
2.2.2.2 router-id 2.2.2.2 is backed off to transmit after 45000ms
Message 2 SYSLOG message for LSA arrival timer (1000 msec in this example)
Mar 15 09:46:06: %STKUNIT0-M:CP %OSPF-4-LSA_BACKOFF: OSPF Process 10,Router lsa id
3.3.3.3 rtrid 3.3.3.3 received before 1000ms time
Router Priority and Cost
Router priority and cost is the method the system uses to “rate” the routers (Figure 20-3). For example, if
not assigned, the system selects the router with the highest priority as the DR. The second highest priority
is the BDR.
Priority is a numbered rating 0 to 255. The higher the number, the higher the priority.
Cost is a numbered rating 1 to 65535. The higher the number, the greater the cost. The cost assigned
reflects the cost should the router fail. When a router fails and the cost is assessed, a new priority number
results.
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