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Subnets basically allow you to take a network, and create sub-networks to increase the amount of addresses available to you. Additionally, it allows you to logically divide your network in to easier to understand, and faster to route, sub networks. There are other benefits, such as faster routing and less network congestion due to additional routers/subnets. I won't list all of 'em.
Lets say you had a 192.168 address. Your network would be 192.168.0.0. You could subnet that out like:
192.168.0.0 -> 192.168.254.254
Or to expand:
192.168.0.0-254
192.168.1.0-254
192.168.2.0-254
192.168.3.0-254
etc.
Your sub networks are the 192.168.1.0, 192.168.2.0, 192.168.3.0...
The subnet mask, then, identifies the subnetwork on which a host communicates, and also the size of the subnet.
Does that help at all? Frankly, I understand all of the concepts here, but I had to do a bunch of googling to figure out how to explain it properly. I hope I did ok :\
Last edited by nachomc; Dec 18, 2007 at 11:39 PM.
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Matt nailed it.
If I can add, think of it as a way to reduce the amount of data you're constantly having to send/route.
If you've got a standard IP, that's 32 bits, right?
192.168.10.50, let's say.
In order to reduce the amount your routing appliances and applications have to reference, your subnet mask breaks down what's assumed for all internal network addresses into a network portion and a host portion. The host portion is what you'd call your subnet; it's what's contained within your masked portion. With your subnet mask, you'd assume 192.168.10, and the 254 routable addresses contained in that network address would be your routable subnet.
So, if you have, in your example, 128.128.128.1 as your full network IP, and a subnet mask of 255.255.255.0, your 128.128.128.x is your network portion, and the x.x.x.1 is your subnet. By using a subnet mask, your routing can essentially ignore the first 24 bits (or 16 bits, or 8 bits, or whatever, based on your subnet mask).
So, if you had larger IP space to manage, you'd do 128.128.x.x, and your subnet mask would be 255.255.0.0. That means your appliance can then bypass the first 16 bits and route using the subnet address.
It's basically a way to say "ignore everything above this level" because it'll be the same. When you're managing thousands and thousands of packets a second, halving the amount of routing data and shortening processing time pays big dividends.
Make sense? That's the way I've always understood it and explained it. I work for Cisco, but I ain't a network guy and don't deal with the stuff regularly and haven't for a while. When you want to talk about fun, ****ed up **** that causes headaches like cnames and a-records for DNS routing, that's when I start shooting people
If I can add, think of it as a way to reduce the amount of data you're constantly having to send/route.
If you've got a standard IP, that's 32 bits, right?
192.168.10.50, let's say.
In order to reduce the amount your routing appliances and applications have to reference, your subnet mask breaks down what's assumed for all internal network addresses into a network portion and a host portion. The host portion is what you'd call your subnet; it's what's contained within your masked portion. With your subnet mask, you'd assume 192.168.10, and the 254 routable addresses contained in that network address would be your routable subnet.
So, if you have, in your example, 128.128.128.1 as your full network IP, and a subnet mask of 255.255.255.0, your 128.128.128.x is your network portion, and the x.x.x.1 is your subnet. By using a subnet mask, your routing can essentially ignore the first 24 bits (or 16 bits, or 8 bits, or whatever, based on your subnet mask).
So, if you had larger IP space to manage, you'd do 128.128.x.x, and your subnet mask would be 255.255.0.0. That means your appliance can then bypass the first 16 bits and route using the subnet address.
It's basically a way to say "ignore everything above this level" because it'll be the same. When you're managing thousands and thousands of packets a second, halving the amount of routing data and shortening processing time pays big dividends.
Make sense? That's the way I've always understood it and explained it. I work for Cisco, but I ain't a network guy and don't deal with the stuff regularly and haven't for a while. When you want to talk about fun, ****ed up **** that causes headaches like cnames and a-records for DNS routing, that's when I start shooting people
Last edited by sybir; Dec 18, 2007 at 11:57 PM.
Matt nailed it.
If I can add, think of it as a way to reduce the amount of data you're constantly having to send/route.
If you've got a standard IP, that's 32 bits, right?
192.168.10.50, let's say.
In order to reduce the amount your routing appliances and applications have to reference, your subnet mask breaks down what's assumed for all internal network addresses into a network portion and a host portion. The host portion is what you'd call your subnet; it's what's contained within your masked portion. With your subnet mask, you'd assume 192.168.10, and the 254 routable addresses contained in that network address would be your routable subnet.
So, if you have, in your example, 128.128.128.1 as your full network IP, and a subnet mask of 255.255.255.0, your 128.128.128.x is your network portion, and the x.x.x.1 is your subnet. By using a subnet mask, your routing can essentially ignore the first 24 bits (or 16 bits, or 8 bits, or whatever, based on your subnet mask).
So, if you had larger IP space to manage, you'd do 128.128.x.x, and your subnet mask would be 255.255.0.0. That means your appliance can then bypass the first 16 bits and route using the subnet address.
It's basically a way to say "ignore everything above this level" because it'll be the same. When you're managing thousands and thousands of packets a second, halving the amount of routing data and shortening processing time pays big dividends.
Make sense? That's the way I've always understood it and explained it. I work for Cisco, but I ain't a network guy and don't deal with the stuff regularly and haven't for a while. When you want to talk about fun, ****ed up **** that causes headaches like cnames and a-records for DNS routing, that's when I start shooting people
If I can add, think of it as a way to reduce the amount of data you're constantly having to send/route.
If you've got a standard IP, that's 32 bits, right?
192.168.10.50, let's say.
In order to reduce the amount your routing appliances and applications have to reference, your subnet mask breaks down what's assumed for all internal network addresses into a network portion and a host portion. The host portion is what you'd call your subnet; it's what's contained within your masked portion. With your subnet mask, you'd assume 192.168.10, and the 254 routable addresses contained in that network address would be your routable subnet.
So, if you have, in your example, 128.128.128.1 as your full network IP, and a subnet mask of 255.255.255.0, your 128.128.128.x is your network portion, and the x.x.x.1 is your subnet. By using a subnet mask, your routing can essentially ignore the first 24 bits (or 16 bits, or 8 bits, or whatever, based on your subnet mask).
So, if you had larger IP space to manage, you'd do 128.128.x.x, and your subnet mask would be 255.255.0.0. That means your appliance can then bypass the first 16 bits and route using the subnet address.
It's basically a way to say "ignore everything above this level" because it'll be the same. When you're managing thousands and thousands of packets a second, halving the amount of routing data and shortening processing time pays big dividends.
Make sense? That's the way I've always understood it and explained it. I work for Cisco, but I ain't a network guy and don't deal with the stuff regularly and haven't for a while. When you want to talk about fun, ****ed up **** that causes headaches like cnames and a-records for DNS routing, that's when I start shooting people
oh...wai.... I work there too... and not as a network tech either :'(
webinar HQ unite!
btw.. hehe
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