Summarizing a block of IP addresses

danb83

How would you go about summarizing the following contiguous block of subnets:

10.48.226.x /25
10.48.227.x /25

all the way through to

10.48.252.x /25


I have the answer as 10.48.224.0 /19, however I am not sure why/how this is.

Any advice would be appreciated.

chX

I'd first convert the IP addresses to binary:

10.48.226.x
10.48.227.x
...
10.48.252.x
___________________________

00001010.00110000.11100010.x
00001010.00110000.11100011.x
...
00001010.00110000.11111100.x


Now compare which bits are similar across all of the addresses (red).

00001010.00110000.11100000.x

Convert it back to decimal:

10.48.224.x

Count the number of bits up until the point they do not all match (the three red bits)

19.

10.48.224.x /19


Hope that makes sense!

chmorin

chX is on the money. That's how you do it.

danb83

chX wrote: »

I'd first convert the IP addresses to binary:

10.48.226.x
10.48.227.x
...
10.48.252.x
___________________________

00001010.00110000.11100010.x
00001010.00110000.11100011.x
...
00001010.00110000.11111100.x


Now compare which bits are similar across all of the addresses (red).

00001010.00110000.11100000.x

Convert it back to decimal:

10.48.224.x

Count the number of bits up until the point they do not all match (the three red bits)

19.

10.48.224.x /19


Hope that makes sense!

cheers, just what I was looking for, a simple explanation.

It seems so straightforward now!

palsantanu71

heyy, i would be really glad if u help me out.
i was studying summarization from todd lammle ccna guide, and one thing was confusing me was this:- summarization of 192.168.144.0/20.
how r we using /20 as a mask in a class c network. doesnt it strts from /24 through /30????
plzz help me out. i m totally confused.

FrankGuthrie

palsantanu71 wrote: »

heyy, i would be really glad if u help me out.
i was studying summarization from todd lammle ccna guide, and one thing was confusing me was this:- summarization of 192.168.144.0/20.
how r we using /20 as a mask in a class c network. doesnt it strts from /24 through /30????
plzz help me out. i m totally confused.

Why could you not use a /20 subnet? By default a Class C network has a /24 subnetmask. If you use /24, you subnetting a Class C network into smaller parts. Using /20 is going the otherway around, making it bigger.