Logic behind giving IP address to a network

Cilia

Hi everyone,

I am preparing for the 640-801 exam and there is one thing my head can see and that is assigning IP address.

When I see the examples in the books I read of routers in a full or partial mesh with ethernet attached to them sometimes even switches,etc,I don't understand in what order to configure the interfaces,I know that routers separate subnets,that is logical to me,but that is all.

I thank in advance any word that might make my brain click.

Regards

Danman32

Switches these days are used to connect one device (host) to one port on the switch and no more. In doing this, you just about eliminate collisions, and provide for the ability to use full duplex, where 2 machines can talk and reply at the same time. Makes for fast data transfers using TCP, since as one host sends a series of blocks of data, the receiving host has to acknoledge each block.

But I am side tracking here. A switch usually will encompass one broadcast domain, which would be a single IP subnet address range. You could add additional switches to add to the port count, or to provide separate connection distribution points.

Although switches eliminate collisions at the layer 2 level, it does nothing for limiting broadcasts, which occur mostly at the layer 3 level, which in turn usually trickles down to requiring level 2 broadcasts. Routers break up networks into separate broadcast regions. So if you have several hosts that talk to each other, and a good portion of the extensive communications is broadcast, you can isolate those machines from others that really don't need to hear those broadcasts. ARP is an example of an IP broadcast that you really can't get away from, though its use is reduced through ARP caching.

How you decide to design your network, such as IP addresses, router placement, and even redundant routing paths, is up to you and the nature of your network. As a CCNA, you won't be called to design a network, but it should be clear if you get a senario question where it may be a good idea to add a router or a switch.

Webmaster

Welcome to the forums!

Try this one:
www.techexams.net/technotes/networkplus/tcpipsuite.shtml

Cilia

Thank you for the input, I am a slow learner but it's digging in.

pizzafart

Let me list a few items that are often assigned individual ip addresses. After each, I will explain the purpose that the address assignment serves. This may not answer all your questions but it might be of use.

1. A computer.
This is easy. A computer needs an IP address so that it can be identified on the network.

2. A router interface.
You are correct, a router is used to seperate networks. Each interface gets an IP address just like a computer does. So, if a router has three active interfaces, it will probably have three different IP addresses. The address that's assigned to an interface is used as the "default gateway" by computers that reside on that network. The address+mask assigned to an interface typically gives away the range of valid addresses used by computers that reside on that network.

So, let's say you have a router with 2 interfaces. On one interface, you could have the following address:

10.0.0.1 /24 (/24 is shorthand for 255.255.255.0)

on the other one, you might have

11.0.0.1 /24

What this means is that your computer and switch address assignments should be between 10.0.0.2 and 10.0.0.254, or 11.0.0.2 and 11.0.0.254, depending on which of the two networks a particular device resides on. Also, the default gateway settings on those devices need to reflect the interfaces address, x.x.x.1 in both cases. Router interfaces tend to get numbers like 1 or 254 but really you could use anything within the confines of the mask.

Note: for this to make 100% sense, you need to understand how subnetting works. It took me a while to figure out subnetting so you may just want to save this post and look at it later on. It also helps to understand how routing tables on routers work.

3. A switch.
A switch may need an ip address so that admins can telnet to it and make configuration changes (and more). This is optional but is usually a good idea unless you like running from wiring closet to wiring closet with a console cable, lol. A switch gets a single address - it does not get addresses per interface like a router does. This is because the switch is layer 2 and doesn't separate layer 3 networks like routers do. This gets a little trickier once you start getting into VLANs but that's off topic for now...

4. Other stuff
Just so you know, this is not an exaustive list of things that could have ip addresses assigned to them.

Maybe this helps? Hopefully I've told you more than just things you already know.