Whats a /29?

[Mr Pickles]

I'm sitting in a meeting and someone says something obtaining a /29 and I'm thinking to myself, "I must have heard that wrong" but sure as anything someone responded with "Are you sure we don't need /24? Because if we do, Cogent will require more documentation" and then I'm like "wtf... they are speaking in /tongues!"

It was in reference to purchasing a new block of IPs. WTF are they talking about?

 

[spidey07]

It's the number of bits in the subnet mask. Also called prefix or CIDR notation.

A /29 is 255.255.255.240. Giving you 14 usable addresses. Normally the larger address block you request the more documentation you have to provide to prove you are actually going to use it. A /24 is just a class C mask - 255.255.255.0 giving 254 usable addresses.

 

[drebo]

Check out CIDR notation.

It's a way to notate subnets in a "short-hand".

 

[Mr Pickles]

Thanks guys, a net admin here sat down with a pad of paper and explained it to me. That CIDR notation helps too.

 

[jlazzaro]

Originally posted by: spidey07
A /29 is 255.255.255.248

i know it was a typo, but i couldnt help myself

 

[cyr0nk0r]

This is an amazing website that helps me ALL the time.

http://www.more.net/technical/netserv/tcpip/subnet.html

 

[jlazzaro]

Originally posted by: cyr0nk0r
This is an amazing website that helps me ALL the time.

http://www.more.net/technical/netserv/tcpip/subnet.html

definately useful, but try to wean off of subnet tables and calculators. force yourself to do the math, and it will eventually become second nature.

 

[cyr0nk0r]

I don't use it enough day to day to memorize things. So when I need to jump on the router and do some changes it's much faster to just throw that page up on my second screen!

 

[spidey07]

Originally posted by: jlazzaro

Originally posted by: spidey07
A /29 is 255.255.255.248

i know it was a typo, but i couldnt help myself

yeah, yeah - I was typing fast. I only counted four fingers, so sue me.