Information Technology Reference
In-Depth Information
Study Guide
Routing Table Structure
The structure or format of the routing table might seem obvious until you take a closer look.
Understanding the structure of the routing table will help you verify and troubleshoot routing issues
because you will understand the routing table lookup process. You will know exactly what the Cisco
IOS does when it searches for a route. The exercises in the following sections focus on the concepts of
level 1 and level 2 routes.
Level 1 and Level 2 Routes
The Cisco IP routing
table
is not a flat database, but a
hierarchical
structure that is used to speed the
lookup process when locating routes and forwarding packets. This structure includes several levels.
For simplicity, we will discuss all routes as one of two levels: level 1 or level 2.
Briefly describe a level 1 route.
A level 1 route is a route with a subnet mask equal to or less than the classful mask of the network
address.
List the three types of level 1 routes.
Default route, supernet route, and network route
List the three sources of level 1 routes.
Directly connected network, static route, and dynamic routing protocol
The level 1 route can be further defined as an ultimate route.
An ultimate route is a route that includes one or both of the following:
A
next
-
hop
IP address
■
An
exit
interface
■
Indicate which of the following routes are level 1 routes by writing “yes” or “no” in the blank in front
of the route.
Level 1 route?
yes
192.168.1.0/24
no
192.168.1.32/27
yes
192.168.4.0/22
yes
172.16.0.0/14
yes
172.16.0.0/16
no
172.16.1.0/24
no
10.1.0.0/16
yes
10.0.0.0/8
