8.1.4 routing tabl
1. Destination type
Each route entry can be classified as a destination type, which can be a network or a router
The network entry is the destination network address of the packet to be forwarded
Router entry router entries to the router router of ABR and ASBR
Through the command show ip os [pf border-routers
In this internal routing table, all destination addresses are ABR and ASBR router ID, and each entry is marked with intra-area I or inter-area I.
two。 Path Typ
* the path within the area where the Intra-area path router is located to reach the destination
* Interregional path A path where the Inter-area path destination is in another area but is still within the OSPF autonomous system.
* external path of type 1 Type 1 external path,E1 destination path outside the OSPF autonomous system
When calculating an external path, the external cost of the route is the sum of the path cost to the ASBR router.
* the external path of type 2 Type 2 external path, the destination is the path outside the OSPF autonomous system.
The cost of the path to the ASBR router is no longer counted when calculating the external path.
OSPF external routes are E2 type routes by default
3. Routing table lookup
(1) choose the route that can most accurately match the destination address
The most accurate match should always be the longest match-the route with the longest address mask
If the route is unreachable, it sends an ICMP unreachable message to the source address of the packet and discards the packet
(2) subtract the set of selectable items by excluding the suboptimal path.
Intra-area path
Interregional path
E1 external path
E2 external path
