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Link-State Advertisements (LSAs)
A link-state advertisement (LSA) communicates the router's local routing topology to all other local routers in
the same area.
The LSA types supported by Dell Networking are defined as follows:
•
Type 1: Router LSA — The router lists links to other routers or networks in the same area. Type 1 LSAs
are flooded across their own area only. The link-state ID of the Type 1 LSA is the originating router ID.
•
Type 2: Network LSA — The DR in an area lists which routers are joined within the area. Type 2 LSAs are
flooded across their own area only. The link-state ID of the Type 2 LSA is the IP interface address of the
DR.
•
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.
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3: connection to a stub network IP network/subnet number.
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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) ensures sufficient time
for sending and resending LSAs and for system acceptance of arriving LSAs. However, some networks may
Open Shortest Path First (OSPFv2 and OSPFv3)
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Troubleshooting
