Administrator Guide

• Type 9: Link Local LSA (OSPFv2), Intra-Area-Prefix LSA (OSPFv3) — For OSPFv2, this is a link-local "opaque" LSA as defined
by RFC2370. For OSPFv3, this LSA carries the IPv6 prefixes of the router and network links.
• Type 11 - Grace LSA (OSPFv3) — For OSPFv3 only, this LSA is a link-local “opaque” LSA sent by a restarting OSPFv3 router during
a graceful restart.
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 network number 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.
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) ensures 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. 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 has been
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 transmit timer
(45000ms) and arrival timer (1000ms).
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
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
Virtual Links
In the case in which an area cannot be directly connected to Area 0, you must configure a virtual link between that area and Area 0.
The two endpoints of a virtual link are ABRs, and you must configure the virtual link in both routers. The common non-backbone area to
which the two routers belong is called a transit area. A virtual link specifies the transit area and the router ID of the other virtual endpoint
(the other ABR).
NOTE: You cannot configure a virtual link through a stub area or NSSA.
Router Priority and Cost
Router 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 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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Open Shortest Path First (OSPFv2 and OSPFv3)