Subnetting Binary and Classses

ally_uk

Hi there

I spent the weekend learning the basic's of binary

( converting ip address's to binary and vice versa)

I want to take the knowledge further

I require easy to read material on IP classes and Subnetting

can anybody help me?

malcybood

good site

http://www.learntosubnet.com/

ally_uk

Ok so far I have understood what a subnet mask is

If you have a IP address by using a subnet mask you can find out the network and node parts of the Ip address

I have learnt binary I know the IP address Classes and default Subnet Classes

But I still cannot get my head around this lol

Can somebody give me the lowdown on the subnetting i'm finding it difficult to grasp the fundementals

why do I need to know the network address?

royal

Read the following thread. It might help you understand subnetting a bit more. If you still have questions afterwards, ask away and I'll do my best to try to help you understand it.

http://www.techexams.net/forums/viewtopic.php?t=16824

ally_uk

Ok First question

what does (2^icon_cool.gif-2=254 mean?

as in the ^ symbol

kujayhawk93

The carat symbol ("^") is used to express an exponential function. For example, 2^8 should be read as "2 to the 8th power".

royal

Binary is base2. Therefore, we use 2^ in our calculations. There are 8 bits in 1 byte. We cannot use 0 or 255 for clients due to broadcast purposes. It is essentially saying that, 2 ^ 8 - 2 = 254. Base 2 to the 8bit power - 2 due to not being able to use 0 or 255 = 254. So if you are assigning a client an address, the last octet should not be a 0 or 255.

If you are doing Class A or B, you can have something like 10.0.0.1 or 10.255.255.1 as a client address. Just as long as you are not using all 0s or all 1s for the client portion, it will be fine.

Hopefully this wasn't too confusing.

ally_uk

Why do we subnet I have read many tutorials and still cannot grasp why we do this?

I know it's to determine the network work address from host address

But why?

Is it because on a network you are given one ISP address so to get all your pcs onto the internet you need to subnet?

Webmaster

Network+ TechNotes wrote:

Instead of using the default subnet masks, additional bits in the mask can be set to 1. This means ‘stealing’ bits from the host portion, which in turn means more bits to create different sub-networks, but each with less available host addresses. This process is known as subnetting. The main reason to divide a Class A, B, or C network into smaller subnets is to use the available address space more efficiently. For example, your company is assigned a Class B network, which allows for 65534 different host addresses. It would be a waste of addresses to use the entire range for a single network with 200 nodes. Instead, the class B address can be subnetted by using Class C subnet mask, or a classless subnet mask.

As you know, there's a limited nr of available IP addresses, hence a limited nr of available IP networks. Whether you use a private IP range or a public one, you'll only have a certain nr of ip addresses available. By subnetting them you can basically override the default subnet mask (class A, B or C mask) and the IP range you're allowed to use into multiple smaller ranges. These networks will need to be connected by a router to allow communication between them.

EdTheLad

There is only a finite number of ip addresses,hence the need for nat and ipv6.
Subnetting saves addresses, imagine you had a class C address 200.10.20.0/24 and you need to address a link between 2 routers, you would use 2 addresses 200.0.0.1 and 200.0.0.2 for instance.That whole class C address 200.10.20.0/24 is wasted on a ptp link.With subnetting you could use a /30 mask that use 4 addresses, 2 for the ports and 2 wasted on the subnet and broadcast address.

ally_uk

Yeah but why overcomplicate things?

Can't I just get by using DHCP and NAT?

EdTheLad

I think you should read about the history of the internet.

ally_uk

In a everyday situation where would you use subnetting though?

I can perfectly setup a network using DHCP

Apart from the how to subnet website are there any other easy to follow guides or tutorials I appreciate you guys trying to help me but your not explaining things that clearly your bombarding me with jargon lol

Webmaster

DHCP has nothing to do with it, that's like comparing apples and oranges. DHCP is protocol for assigning addresses automatically, but whether you assign address automatically or manually doesn't matter for the concept of subnetting. DHCP is a luxury to reduce work for admins, but subnetting a necessity. Without subnetting there simply wouldn't be enough IP addresses (at least not until IPv6 becomes more common). Even subnetting was eventually not enough, so they created NAT (the security NAT offers is just and added advantage), which allows the same IP (sub-)networks to exist in the same internetwork/wan. It's however not a replacement for subnetting, it's another method to get more out of the available IP address space. When they originally create IPv4 they never expected some day so many computers/devices would use it.

www.techexams.net/technotes/networkplus/tcpipsuite.shtml
www.techexams.net/technotes/networkplus/internetconnections.shtml

www.mcmcse.com also has a good article on subnetting.

In a everyday situation where would you use subnetting though?

When you don't have enough 'IP networks' to accommodate for every network in your WAN/'Internetwork' and hence need to subdivide those IP networks into smaller networks. So for example, when you have one Class C IP network available, let's say 192.168.20.0 255.255.255.0, but need to create 4 different IP networks. (for example 4 LANs connected to each other by one or more routers)

malcybood

ally_uk wrote:

In a everyday situation where would you use subnetting though?

I can perfectly setup a network using DHCP

Apart from the how to subnet website are there any other easy to follow guides or tutorials I appreciate you guys trying to help me but your not explaining things that clearly your bombarding me with jargon lol

Ally,

The above would not appear as jargon if you had grasped the concept and read some background info on subnetting and IP addressing.

I don't think you've looked hard enough, there are thousands of resources on the web in regard to this topic. I done a google search on "Class B subnetting" and got loads of web pages one of which contained the following:

Google search - http://www.google.co.uk/search?hl=en&q=class+b+subnetting&meta=

Subnetting Website http://www.swcp.com/~jgentry/topo/unit3.htm

2. Reason for Subnetting
We said that the default subnet mask for a class A IP network is 255.0.0.0. Once octet only of a class A network address identifies the network, with this subnet mask. This leaves three octets of 8 bits each, or 24 bits, to identify the host on that one network. 2^24=16,777,216 addresses. Two addresses are reserved, x.x.x.0 and x.x.x.255. 16,777,214 nodes can be assigned an IP address on this network.

It is highly unlikely that any organization would want one network of 16,777,214 nodes. They might want that many devices connected in a wide area network (WAN), thus capablee of communicating when neccessary, but they will want to subdivide this huge network into mostly self-contained subnetworks of nodes that communicate with each other often. This is called subnetting.

To understand why, consider what would happen in either a broadcast or a token passing network that consisted of over 16,000,000 nodes. Nothing would happen. It simply would not work. Though the problem is not as drastic, class B and class C IP networks are often subnetted, also.

The subnet mask is used to subdivide an IP network into subnets. This is a division that takes place in OSI layer 3, so it is a logical division that is created by the addressing scheme. This logical division is usually combined with a physical division. Many subnets are physically isolated from the rest of the network by a device such as a router or a switch. This aspect of subnetting is discussed in Unit 3--Data Link Layer.

If you still feel you can't understand the concept of subnetting I sugget the Todd Lammle CCNA sybex 5th Edition book as there is a clear explanation in there of subnetting and VLSM or use the links that the webmaster and co have provided.

I also googled "subnetting explained" and it came up with loads.....surely one of these resources must be able to help you?

Regards

Malc

ally_uk

I put together a Subnetting Bible document using the following website

http://www.semsim.com/ccna/tutorial/subnetting/subnetting.html

I'm going to go over the material in my own time and see how I get on

The remaining question I put to you guys is where the hell does the IP address come from in which you want to subnet

for example if I have a small network of 8 computers with a router connected to the internet would I subnet the IP address provided by the ISP???

This is the part I cannot get my head around

royal

ICANN assigns ip addresses to service providers, which includes ISPs. From there, ISPS assign you ip addresses. The thing is, since ip addresses are finite as others have stated, ICANN will give some service providers a portion of Class A addresses and Class B addresses since there are so many ip addresses. So lets say ICANN gives Comcast Class A address range that is /10. So instead of Comcast now having 2^24-2=16,777,214 client ip addresses, they will 2^22-2=4,194,302. That's a reduction of 12,582,912 ip address just by removing 2 bits from the client portion! Those remaining ip addresses could be used for another service provider instead of just giving Comcast that whole entire Class A range.

malcybood

ally_uk wrote:

I put together a Subnetting Bible document using the following website

http://www.semsim.com/ccna/tutorial/subnetting/subnetting.html

I'm going to go over the material in my own time and see how I get on

The remaining question I put to you guys is where the hell does the IP address come from in which you want to subnet

for example if I have a small network of 8 computers with a router connected to the internet would I subnet the IP address provided by the ISP???

This is the part I cannot get my head around

No you would subnet the ip address range of your internal LAN to accomodate the multiple hosts/networks that YOU have not the ISP. There are private address ranges that will never be "bought or leased from an isp" reserved for internal LAN and WAN connectivity. These are typically subnetted by companies to accomodate multiple sites/client machines:

A Class: 10.0.0.0 - 10.255.255.255
B Class: 172.16.0.0 - 172.31.255.255
C Class: 192.168.0.0 - 192.168.255.255

It is up to you which network you choose and how you subnet it. By using NAT you can set your network up so it may appear as 83.56.50.93 on the ISP side but 10.10.10.0 internal network on the LAN/WAN side. This is done in the router configuration

You would work out how you subnet your network and how many bits to borrow by thinking about the following.....

How many networks do I need?
How many hosts do I need on each network?
How much scalability do I need?

Example:
Q. You have decided to use the Class C private network address 192.168.1.0 and you require 4 networks that have 25 hosts each for your internal lan. What would be a suitable borrow?

A. a 3 bit borrow is appropriate as this would give you 8 subnets (7 usable with IP Subnet Zero enabled) each with 30 usable hosts

As long as the TCP/IP address settings are setup correctly on your PC's and routers are correctly configured all hosts on your network will be able to communicate with each other despite being on different subnets.

Does this make sense to you?

Also check this out: http://en.wikipedia.org/wiki/Private_network

Kaminsky

Apart from the finate range of IP addresses which is probably the most important need for subnetting, another cause for subnetting is keeping seperate departments completely seperate on the network. Subnetting is also good for planning how you assign your IP addresses throughout your organisation allowing you to keep control of what addresses get assigned where. Also, it can help with broadcast domains so that they only shout within their own departmental network and don't interfere with other departments traffic.

Imagine you had HR, Finance and Sales departments. You have them all networked up but don't necessarily want them to see each other on the network. Subnetting is just one way of restricting what they see and it can also help the IT admin with IP address assignments.

You could do this in different ways like VLANing, etc. So you could have HR in the 192.1.1.(1-255)/24 range. Finance in the 192.1.2.(1-255)/24 range, etc. Now unless you put routes in the router tables and access lists permissions, a host in one department won't be able to see any host in the other department. Those departments are completely invisable in networking terms as they are on different subnets.

Hope that explanation helps you a little in why we have subnetting in the first place.