Refer to the exhibit. Which address and mask combination represents a summary of the routes
learned by EIGRP?
A.
192.168.25.28 255.255.255.240
B.
192.168.25.0 255.255.255.252
C.
192.168.25.0 255.255.255.240
D.
192.168.25.16 255.255.255.252
E.
192.168.25.28 255.255.255.252
F.
192.168.25.16 255.255.255.240
Explanation:
On very large networks, there may be hundreds or even thousands of individual networks and
subnetworks being advertised. All these routes can be very taxing on a router’s memory and
processor. For example, routers on the Internet were starting to be overwhelmed with a couple of
hundred thousand routes. After summarizing routes and using CIDR, the number of routes has
been dramatically reduced.
Examine the table to determine the maximum number of bits (starting from the left) that all of the
addresses have in common. (Where they are lined up, we boldfaced them to make them easier for
you to see.) The number of common bits is the prefix length for the summarized address (/20).
In this example, we can see from the table that all of the addresses have the first 20 bits in
common. The decimal equivalent of these first 20 bits is 172.16.96.0. So, we can write our new
summarized address as 172.16.96.0/20. If we were to later add a network 172.16.98.0, it would
need to be behind the router summarizing this address space. If we didn’t, it could cause
problems.