Understanding IP Block allocation

This is cross posted from WHT with permission from the original poster there. While most of us likely know or look it up in a pinch, I thought it'd be nice to have here for reference too. When you read someone say, "I need a server with a /XX block of IPs" or talking about a provider acquiring a new large block of addresses, this little chart can help put it in perspective.


    CIDR block IP range (network - broadcast) Subnet Mask IP Quantity

61.245.172.23/32 61.245.172.23 - 61.245.172.23 255.255.255.255 1
61.245.172.22/31 61.245.172.22 - 61.245.172.23 255.255.255.254 2
61.245.172.20/30 61.245.172.20 - 61.245.172.23 255.255.255.252 4
61.245.172.16/29 61.245.172.16 - 61.245.172.23 255.255.255.248 8
61.245.172.16/28 61.245.172.16 - 61.245.172.31 255.255.255.240 16

61.245.172.0/27 61.245.172.0 - 61.245.172.31 255.255.255.224 32
61.245.172.0/26 61.245.172.0 - 61.245.172.63 255.255.255.192 64
61.245.172.0/25 61.245.172.0 - 61.245.172.127 255.255.255.128 128

61.245.172.0/24 61.245.172.0 - 61.245.172.255 255.255.255.0 256
61.245.172.0/23 61.245.172.0 - 61.245.173.255 255.255.254.0 512
61.245.172.0/22 61.245.172.0 - 61.245.175.255 255.255.252.0 1024
61.245.168.0/21 61.245.168.0 - 61.245.175.255 255.255.248.0 2048
61.245.160.0/20 61.245.160.0 - 61.245.175.255 255.255.240.0 4096
61.245.160.0/19 61.245.160.0 - 61.245.191.255 255.255.224.0 8192
61.245.128.0/18 61.245.128.0 - 61.245.191.255 255.255.192.0 16384
61.245.128.0/17 61.245.128.0 - 61.245.255.255 255.255.128.0 32768
61.245.0.0/16 61.245.0.0 - 61.245.255.255 255.255.0.0 65536

61.244.0.0/15 61.244.0.0 - 61.245.255.255 255.254.0.0 131072
61.244.0.0/14 61.244.0.0 - 61.247.255.255 255.252.0.0 262144
61.240.0.0/13 61.240.0.0 - 61.247.255.255 255.248.0.0 524288
61.240.0.0/12 61.240.0.0 - 61.255.255.255 255.240.0.0 1048576
61.224.0.0/11 61.224.0.0 - 61.255.255.255 255.224.0.0 2097152
61.192.0.0/10 61.192.0.0 - 61.255.255.255 255.192.0.0 4194304
61.128.0.0/9 61.128.0.0 - 61.255.255.255 255.128.0.0 8388608

61.0.0.0/8   61.0.0.0 - 61.255.255.255     255.0.0.0 16777216
60.0.0.0/7   60.0.0.0 - 61.255.255.255      254.0.0.0 33554432
60.0.0.0/6   60.0.0.0 - 63.255.255.255     252.0.0.0 67108864
56.0.0.0/5  56.0.0.0 - 63.255.255.255      248.0.0.0 134217728
48.0.0.0/4  48.0.0.0 - 63.255.255.255      240.0.0.0 268435456
32.0.0.0/3  32.0.0.0 - 63.255.255.255      224.0.0.0 536870912
0.0.0.0/2  0.0.0.0 - 63.255.255.255     192.0.0.0 1073741824
0.0.0.0/1  0.0.0.0 - 127.255.255.255      128.0.0.0 2147483648

Original thread: http://www.webhostingtalk.com/showthread.php?t=1322901

Other tools to do the same: http://services.quadranet.com/utilities/ip , http://www.ipaddresslocation.org/subnet-mask-calculator.php , http://jodies.de/ipcalc , and http://www.subnet-calculator.com/ .

I've used the Quadranet one more times than I can count.

Thank you for posting as a chart. Normally I use subnet-calculator.com

This is just a thinly veiled advertisement for ... Sri Lanka Telecom? <_<

My go-to resource for anything I can't do in my head quickly is this subnet cheat sheet.

scv said:

This is just a thinly veiled advertisement for ... Sri Lanka Telecom? <_<

My go-to resource for anything I can't do in my head quickly is this subnet cheat sheet.

Click to expand...

We apparently use the same cheat sheet. +1

But yeah, never needed anything else, it's easy enough to calculate once you have the netmask. And even that's something I'm sort of really used to these days, since I've deployed so many boxes already.

scv said:

This is just a thinly veiled advertisement for ... Sri Lanka Telecom? <_<

My go-to resource for anything I can't do in my head quickly is this subnet cheat sheet.

Click to expand...

I use that one usually, I've used THIS one in the past for IPv6 stuff when explaining IPv6 to clients, easier to link that

I would prefer to refer to the RFCs - http://www.ietf.org/rfc/rfc1878.txt

Still, thanks for the thread though.

Wintereise said:

We apparently use the same cheat sheet. +1

But yeah, never needed anything else, it's easy enough to calculate once you have the netmask. And even that's something I'm sort of really used to these days, since I've deployed so many boxes already.

Click to expand...

I use my brain these days. Have done it so many times that it's just stuck in.

scv said:

This is just a thinly veiled advertisement for ... Sri Lanka Telecom? <_<

My go-to resource for anything I can't do in my head quickly is this subnet cheat sheet.

Click to expand...

Wintereise said:

We apparently use the same cheat sheet. +1

But yeah, never needed anything else, it's easy enough to calculate once you have the netmask. And even that's something I'm sort of really used to these days, since I've deployed so many boxes already.

Click to expand...

What a small world, I used that too, back in CCNA days

Good cheat sheet! Thanks

This is nice one to get the CIDR block from a specific IP:

whois xxx.xxx.xxx.xxx | grep CIDR

tonyg said:

This is nice one to get the CIDR block from a specific IP:

whois xxx.xxx.xxx.xxx | grep CIDR

Click to expand...

This only works for addresses in certain registries, mostly ARIN. You'll have some trouble with RIPE, APNIC, etc.

Nice share, how about this one?

Well, I prefer the cheat sheets from Packet Life @ http://packetlife.net/library/cheat-sheets/