TOPIC: pc technician who's boss won't explain things to him ..

i've tried to get him to explain to me why we are on a 255.255.255.240 subnet mask .. but he won't ..

i do know that our provider mentioned something about a 240 subnet mask .. but, it didn't make sense to me .. how many IP's can we dish out using DHCP with a 240 subnet mask?? would the 240 subnet mask limit the number of clients we could have online/connecting to the internet at one time??

again, i just work here .. i'm just try'n to learn more about networking .. unfortunately .. nobody here at work is willing to explain ..

i'll prolly spend the rest of the day reading/checking out this site .. i've already learned more from this site in 30 minutes than i have working at this job for the past 3 months

Raggedy,

Let me (on behalf of our team) firstly welcome you to Firewall.cx.

When one is keen on learning but discouraged from the people he is surrounded, its possibly the worst thing that can happen to him, as its like cutting the wings off a bird that wants to learn how to fly.

Don't worry though cause the team and members of this site will gladly spend their valuable time to help you and everyone else - that's why we are here.

Subnetting is a big topic, but also a very easy one once you learn how to tackle it. I am not aware of your experience, so I'll keep the explanation as simple as possible.

You mentioned that your ISP gave you a subnetmask of 255.255.255.240, and from your question, I am assuming that this subnetmask has also been applied to your internal network;

So what effect will the above subnetmask have in a network when it's applied ?

The purpose of using subnet masks is to partition (split) our network into smaller pieces, making it easier to manage and also increasing security access to specific portions of that network.

Small networks usually use the standard 255.255.255.0 subnet mask (also called - "default subnet mask") since they have a very simple structure and are rarely required to be partitioned.

I would not be able to answer you as to 'why' your boss has chosen to apply this subnet mask to your internal network (he might not be sure himself!), but I'll explain what it does.

The default subnetmask I mentioned above (255.255.255.0) will give your network the ability to host upto 254 hosts (computers) or if you like, IP addresses. This means you can allocate upto 254 IP addresses to this network.

The 255.255.255.240 subnet mask, when applied, will partition your network, that is, create 16 smaller networks, and each network will be able to have a total of 14 IP addresses.

Let's compare them to get the big picture:

Subnetmask 255.255.255.0 = 1 network with 254 usable IP Addresses:

(assuming 192.168.0.0 is our network)
Network 1 = 192.168.0.0
Range: 192.168.0.1 (first available IP) to 192.168.0.254 (Last available IP)


Subnetmask 255.255.255.240 = 16 networkswith 14 available IP addresses:

(Assuming 192.168.0.0 is out network)
Network 1 = 192.168.0.0
Range: 192.168.0.1 (first available IP) to 192.168.0.14 (last available IP)


Network 2 = 192.168.0.16
Range: 192.168.0.17 (first available IP) - 192.168.0.30 (last available IP)


Network 3 = 192.168.0.32
Range: 192.168.0.33 (first available IP) - 192.168.0.46 (last available IP)


Network 4 = 192.168.0.48
Range: 192.168.0.49 (first available IP) - 192.168.0.62 (last available IP)

Network 5 = 192.168.0.64
Range: 192.168.0.65 (first available IP) - 192.168.0.78(last available IP)
....and so on..


As you can see, we have smaller networks with fewer IP's in each one.

I'm hoping this answers your question, if not, just let us know specifically what you need clarified and we will provide the best answer for you!

Since it seems like your new to subnetting, we have one of the best tutorials available in the world (seriously). Check it out and I'm sure it will help you understand everything on the topic.

Cheers,

Thank you for the explanation. I'm reading the tutorial now as I flick back and forth between the forums. I'm trying to understand how our network is setup and why. You explained exactly what I was wanting to know.

So basically, using the DHCP program in W2k .. all he did was go in and create 16 scopes?? With 14 IP's per scope.

See, I work for a small wireless company. I do the installs and he tells me which way to configure the clients (DHCP or a static) but nothing else.

Anyways, we just got a new drop from our provider for a new area to which I am currently located. Since I'm here for the beginning of the creation of this network, I figured now would be the best time to gain a better understanding of how it all works.

I know how to read/convert the bits/bytes into IP's, but, I'm still a little confused as to why we would need that many different "mini" networks?? Any reason why a ISP would want to do that?? Instead of using one large pool of IP's to choose from??

As far as networking goes .. I've got very limited experience. I've setup my own mini networks at home using a router (the 50$ linksys kind).

Also, how do you read the icons on the DHCP page of W2K server? Some have icons with what appears to be the corel word perfect icon on top of the computer icon .. give me a few .. i'll post a link to a pic

www.angelfire.com/blues2/raggedy_hobo/images/icon.bmp ..

when i try to ping any ip address associated with such an icon .. i get destination net unreachable

see, we have a T1 provider at this new location .. they provide the support/config for the router on the WAN side that connects us to the internet .. matter of fact, they have 100% control over it .. we have none (which is extremely nice since they do all the configuring for us .. my boss simply tells them what we want/need)

from there, we go to our Access Point located on top of a tower which has several antenna's on it .. our customers receive there signal via wet11's (2.4GHz wireless ethernet bridges) from which a cat5 is ran to there computer or router .. and we shoot the signal to other towers located at varying distances ..

on a side note .. i've complained til i'm blue in the face about cat5 cabling and that you shouldn't run cat5 cable longer than 120ft .. else you get packet loss due to attenuation .. but, my boss won't listen to me .. am I correct??

Raggedy,

I really can't answer as to why you ISP have given you that specific subnetmask. What I can tell you, is that depending on the IP's a customer requests, the ISP will supply the appropriate number of IPs using various subnetmasks.

As far as Cat 5 ethernet, there is a whole section dedicated to it. The maximum length a Cat5 cable should run is 100 meters. I've seen it work at 125 and 140 meters, but its a risk.

Coming to the DHCP screenshot, Its been a while since I used MS's DHCP server and I can't honestly remember. I'll be required to muck around with it soon for my last MCSA exam, but until then, I don't plan on installing and using it. Perhaps one of our members will be kind enough to explain that part.