640-802 CCNA Study Guide - Elktech.org

Cisco 640-802 Exam
Routing protocols summarize or aggregate routes based on shared network numbers within the
network. To calculate the summarized route of the router, it is necessary to determine how many
bits on the left of those addresses are the same. The steps are shown below:
Step onE. Convert addresses to binary format and align them.
Step two: Find out the identical last bit of all addresses.
Step threE. Calculate how many bits are the same. The summarized route is an IP address with a
slash, which will be helpful.
172.16.12.0/24= 172.16.000011 00.00000000
172.16.13.0/24= 172.16.000011 01.00000000
172.16.14.0/24= 172.16.000011 10.00000000
172.16.15.0/24= 172.16.000011 11.00000000
172.16.15.255/24= 172.16.000011 11.11111111
The first 22 bits of IP addresses 172.16.12.0---172.16.15.255 are identical, so the best
summarized route is 172.16.12.0/22.
Using route summary can reduce the routing items on the summarized router to decrease the
memory occupied and network traffic generated by routing protocol.
Route summary implementation:
A. The bits on the left of multiple addresses must be identical.
B. Routing protocol should select route according to the 32-bit IP address and the prefix length of
the maximum 32 bit address.
C. Routing update must contain 32-bit IP address and the prefix length (subnet mask)
QUESTION NO: 197
The show interfaces serial 0/0 command resulted in the following output. Which three are possible
reasons for this interface status? (Choose three.)
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