Setup Guide

● Type 3: Summary LSA (OSPFv2), Inter-Area-Prefix LSA (OSPFv3) — An ABR takes information it has learned on one
of its attached areas and can summarize it before sending it out on other areas it is connected to. The link-state ID of the
Type 3 LSA is the destination network number.
● Type 4: AS Border Router Summary LSA (OSPFv2), Inter-Area-Router LSA (OSPFv3) — In some cases, Type
5 External LSAs are flooded to areas where the detailed next-hop information may not be available. An ABR floods the
information for the router (for example, the ASBR where the Type 5 advertisement originated. The link-state ID for Type 4
LSAs is the router ID of the described ASBR).
● Type 5: LSA — These LSAs contain information imported into OSPF from other routing processes. They are flooded to all
areas, except stub areas. The link-state ID of the Type 5 LSA is the external network number.
● Type 7: External LSA — Routers in an NSSA do not receive external LSAs from ABRs, but are allowed to send external
routing information for redistribution. They use Type 7 LSAs to tell the ABRs about these external routes, which the ABR
then translates to Type 5 external LSAs and floods as normal to the rest of the OSPF network.
● Type 8: Link LSA (OSPFv3) — This LSA carries the IPv6 address information of the local links.
● 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
NOTE:
The sequence numbers are reset when previously cleared routes that are waiting for the LSA throttle timer to expire
are re-enabled.
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.
Open Shortest Path First (OSPFv2 and OSPFv3)
545