Subneting Problem----Pls help

Unanswered Question
Oct 7th, 2007

I have a small problem ..maybe for you guys its very easy but for me its kind of difficult...for example if you have 3 routers with 1 host each and 2 switches(no hots).you need to assign ip addresses to the routers and switches.One router its partial configured with ip and mask(192.168..../28) and we have to chose from 4 ip's Class C(192.168.../30 /27 /28 /29) witch ip to assign to the other routers and you now witch ip goes to routers and witch goes to the switches.I know its something about subneting but I dont know now how to solev it......thank you very much

I have this problem too.
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sgregg Sun, 10/07/2007 - 17:55

Dont forget the first IP is the network IP and the last is the broadcast, you cannot use those to Ip a physical device. So first available IP in each subnet you can use to IP your router interface and you can start IP'ing your hosts with the very next available IP in that subnet. For example->

sn#2- = network address = Router IP /27 mask = host ip /27 with a default gateway of (The router) = broadcast

Do the same for the last 2 host subnets.

Next lets talk about the first subnet- >


This is the ip range we will use to connect your routers together. We dont need 30 usable IP addresses to be wasted on a network that has a point to point connection and will have no more than 2 devices. So we are going to further subnet this down with a /30 which is common for a point to point (p2p) connection such as that between 2 routers. /30 gives you 4 ip addresses with 2 usable hosts. So your range will go from this->

to this->

and so on until you get to .31

All we need for these 3 routers are 2 of these subnets so take the first 2.

your first router pair will be ip'd as follows. = network = Router 1 = Router 2 = broadcast

These will have a /30 aka subnet mask.

I really recommend that you use entirely different subnets to connect your routers but still use the /30 mask. For instance I would also recommend that you use an entire class c per subnet because this is an ideal size and will allow room for growth and hurts nothing, with private addressing you have plenty of room to play around.

I hope this at least clears up a little confusion regarding subnetting for you.


quantico24 Sun, 10/07/2007 - 20:09

Thank you so much Shawn for the I understood something from what you said but how about the switches ...what ip's I will assign ....

rayroyaleverest Mon, 10/08/2007 - 09:43

You will assign the switch an IP address from the subnet to which the switch belongs.

sgregg Tue, 10/09/2007 - 09:31

Technically you are better off to IP the switches from an entirely different subnet as well and call this your management network. All of your switches management IP can be in the same subnet as one another even if they are supporting many other subnets. Typically you see switches many times in the same subnet as your hosts but this is not a good design practice. So if you want, just give them an IP out of your host subnet (Do not use the switch IP as your default gateway). If you want to practice implementing this in a more appropriate fashion, use a management vlan (By default vlan1 in 802.1q) and if you want to practice good security measures change the management vlan from something other than VLAN1. I realize this is more than you asked and for ease you can use one of your ip's from your host subnet but I just wanted to make you at least aware of the big picture.



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