CCNA - Cisco Routing Table Review Notes

The routing table is not just a list of routes. The routes are stored in a hierarchical structure, storing the routes in this way has the benefit of speeding up table lookups.  Even though the routing table handles both classful and classless addressing, it is still built around the classfull addressing.  

Level 1 Routes  

-A level 1 route is a route with a subnet mask equal to or less than the classful mask of the network address. 

-The source of the level 1 route can be a directly connected network, static route, or a dynamic routing protocol. 

-If a level one route includes a next hop or exiting interface then it can be classified as a ultimate route 

-If the level one route does not include a next hop or exiting interface it is a parent route  

-The classful subnet mask is always displayed in the level 1 route  

Level 2 Routes  

-A level 2 route is a route that is a subnet of a classful network address  

172.16.2.0 and 172.16.3.0 are both Level 2 routes  

-If a level 2 route is not using its classful subnet mask and is configured with a VLSM mask the individual Level 2 routes  will be displayed with the  subnet masks for their  corresponding networks while the Level 1 parent route will be displayed with the classful subnet mask 

 

Classless and classfull Routing behaviors are not the same as classless and classfull routing protocols. Classfull and classless routing protocols affect how the routing table is populated. Classfull and classless routing behaviors determine how the routing table is searched after it is populated.