ISIS-Routing Area Routes of Three Types of Routers

The routing characteristics of Level-1 routers are as follows:
· Only the Level-1 LSDB is available.
· The link state database contains only the local router LSP.
· There is no routing information about other areas in the routing table.
· There is a default route in the routing table, and the next hop is a Level-1-2 router.

The routing characteristics of Level-2 routers are as follows:
The · Level-2 router has only the Level-2 LSDB.
· The LSDB contains the LSP of the router in the backbone area, but no LSP is generated by the Level-1 router.
· The routing table contains the routing information of the entire network.

The routing characteristics of Level-1-2 routers are as follows:
A ·Level-1-2 router has a Level-2 LSDB and a Level-1 LSDB.
The · Level-1 database contains LSPs in the local area, and the Level-2 database contains LSPs in the backbone area.
The ATT bit is set to 1 in the Level-1 LSP generated by itself.
· The routing table contains the routing information of the entire network.