For all LSA types, there are 20-byte LSA headers. One of the fields of the LSA header is the link-state ID.Each router link is defined as one of four types: type 1, 2, 3, or 4. The LSA includes a link ID field that identifies, by the networknumber and mask, the object this link connects to.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 the DR.• 3: connection to a stub network IP network/subnet number.• 4: virtual link neighboring router ID.LSA ThrottlingLSA throttling provides configurable interval timers to improve OSPF convergence times.The default OSPF static timers (5 seconds for transmission, 1 second for acceptance) ensures sufficient time for sending andresending LSAs and for system acceptance of arriving LSAs. However, some networks may require reduced intervals for LSAtransmission and acceptance. Throttling timers allow for this improved convergence times.The LSA throttling timers are configured in milliseconds, with the interval time increasing exponentially until a maximum time hasbeen reached. If the maximum time is reached, the system, 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, as shown below for the transmittimer (45000ms) and arrival timer (1000ms).Mar 15 09:46:00: %STKUNIT0-M:CP %OSPF-4-LSA_BACKOFF: OSPF Process 10,Router lsa id2.2.2.2 router-id 2.2.2.2 is backed off to transmit after 45000msMar 15 09:46:06: %STKUNIT0-M:CP %OSPF-4-LSA_BACKOFF: OSPF Process 10,Router lsa id3.3.3.3 rtrid 3.3.3.3 received before 1000ms timeNOTE: The sequence numbers are reset when previously cleared routes that are waiting for the LSA throttle timer toexpire are re-enabled.Router Priority and CostRouter priority and cost is the method the system uses to “rate” the routers.For example, if not assigned, the system selects the router with the highest priority as the DR. The second highest priority is theBDR.• 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 shouldthe router fail. When a router fails and the cost is assessed, a new priority number results.Open Shortest Path First (OSPFv2 and OSPFv3) 581
