OSPF LSA Types
LSA Type to Route Type
| Number | Route | RFC Name | Purpose | Description |
|---|---|---|---|---|
| 1 | O | Router-LSA | interfaces on a router | Flooded, Single Area, never crosses area boundary |
| 2 | O | Network-LSA | routers on a network | Flooded, Single area, only sent by the DR |
| 3 | O IA | Summary-LSA | networks in other areas | ABRs send these, to describe, routes to networks |
| 4 | E1, E2 | Summary-LSA | next-hop to a ASBR | ABRs send these, to provide reachability for ASBRs |
| 5 | E1, E2 | AS-external-LSA | routes to E1 or E2 networks | ASBRs send these, to describe, routes to an AS |
| 7 | N1, N2 | NSSA Summaries | routes to N1 or N2 networks | NSSA ASBRs send these, to describe, routes to an AS |
Format
The Router ID is what is used to build the SPT. It’s very important it’s both
- Correct
- Easy to identify the router
+-------------------------+ Three fields to differentiate LSAs
| LS Age | - LS Type
+-------------------------+ - Link State ID
| Options LS Type | - Advertising Router
+-------------------------+
| Link State ID | < -- Unique number from the Advertising Router for Each LSA
+-------------------------+
| Advertising Router | < -- Router ID
+-------------------------+
| LS Sequence Number | < -- How old the LSA is. LSAs with higher numbers are updates to older LSAs
+-------------------------+
| LS Checksum |
+-------------------------+
| Length |
+-------------------------+