Summarizing Routes

control

Been Looking through some examples and seeing If I could get the summary right, testing with online calculator, but struggling with this one..

How would I go about summarizing the following routes?

10.55.4.0/25
10.55.4.128/25
10.55.5.0/25
10.55.5.128/25

10.55.4.0/23 is correct apparently....how do you get to this?

boredgamelad

Convert the routes to binary and put them in a list:

00001010.00110111.00000100.00000000
00001010.00110111.00000100.10000000
00001010.00110111.00000101.00000000
00001010.00110111.00000101.10000000

Locate the place where the common bits between all routes ends:

00001010.00110111.00000100.00000000
00001010.00110111.00000100.10000000
00001010.00110111.00000101.00000000
00001010.00110111.00000101.10000000

Count the number of common bits: 8 + 8 + 7 = 23. This number tells you which subnet mask to apply to the first IP address in the block, giving you 10.55.4.0/23.

grechy

10.55.4.0/25
10.55.4.128/25
10.55.5.0/25
10.55.5.128/25

25 and 25 = 24
25 and 25 = 24
24 and 24 = 23

Works for most things.

richypc

I learned to do these in my head. If you get one of these they should be easier than this one, one which will be very easy to do without writing all of those 1s and 0s.

Don't get me wrong, writing out the 1s and 0s help you understand it and grasp it.