atcomsystems.ca/forum Forums VOIP Phones & IP PBX Networking IP Addressing and Subnets.

Well, I am not trying to hijack the entire catagory, but I figure going to the experts is needed.

So I need some clarification of the way IP address and Subnets work together in regards to private networks.

So in a private network, The most IP addresses you can have in any one range is 255, correct? Meaning 192.168.0.1 thru 192.168.0.255. All machines in this range can send data back and forth to each other. They all have a subnet of 255.255.255.0

Now lets say you needed more addresses than just the 255. Lets say you had 500 computers or even 500 IP phones that needed to talk to one another. What do you do? How exactly do the IP range and subnet range work together. I have done some online research, but it still isn't clear.

Now the second part of this question is you have 500 computers, but 50 of them are in HR and they still need to communicate, but they need protection too. Is this where they get there own SUBNET ?

I appreciate anyone who can enlighten me.

Z-man

In theory you can increase a class c network past 254 however, the best way would be to change to a class b ip scheme.

I don't really know---for any of my IT questions--I just hand it over to JJ from our sister company (Rockford IT). But from what he has told me when he "baby talks" to me---you change the IPconfig to mask being 255.255.0.0--then you can have a maximum of 64514 computers. The range would be 192.168.x.x to 192.198.254.254.

Now, I don't know if this is correct, because I'm just remembering, here. A couple of years ago, he took pity on me and slowly went through the "math" of IP addresses with me.

Hopefully, someone who really know their stuff can add to this.

This is a very complex subject that I could spend days writing about. Id recommend going to Youtube and searching for IP address basics. There you'll find hundreds of videos covering just about everything about TCP/IP.

For the first question yes you could increase the size of the network by subnetting or switching the network class.

The second question is to protect or isolate certain groups of computers you would use VLANs.

The subnet mask tells the device whether the address its trying to reach is local. It does this by looking at its own IP address and at the subnet mask. If the subnet mask is 255.255.255.0 for example then the device knows that the first three octets are local if they are identical to the devices IP address. If the device has an ip address of 192.168.0.25 then 192.168.0 is the local network. 192.168.0.2 192.168.0.58 192.168.0.201 are all local. If the device is trying to reach 192.15.0.1 then it looks and sees that the second octet is 15 and not 168 and it knows that this address is not local and must be sent to the gateway. If the subnet mask was 192.168.0.0 then now you have the possibility to have 65536 hosts because everything from 192.168.1.1 to 192.168.254.254 is local to a pc having an address of 192.168.x.x.

so, if on my local network, I put in a subnet of 255.255.255.248, does this mean I can only use the first 248 IP addresses?

Also, did I mis-speak when I said a limit of 255 addresses, when it is actually 256 because you count 0 as an address so 0-255?

0 and 255 are not typically used for addresses so you would use 1-254. There are a couple of special cases but for your purposes just know that you can use 1-254. If you use 248 you can only have 8 hosts. That's subnetting and more advanced than basic addressing. To keep things simple for you just know that the 255 means that octet on the device must match. so 255.0.0.0 means that a pc with an address of 192.x.x.x is on the same network. Any device 192. something is on the same network but any other number in the first octet means its a different network. So an address of 191. would be on a different network. For most purposes you would use either an a, b, or c subnet mask which are 255.0.0.0 255.255.0.0 and 255.255.255.0

If a network needs more then 254 hosts (devices), they will change the network to class B network. I have hear that supernetting is possible to get more IP address withing a network, but most will aether use VLans or use a Class B addressing. I have not actually seen a class C used with a class B subnet mask. All the network classes I took (online and in class)mention supernetting or Classless routing, but don't say why or why not to do this.

Anyway, I aggress with tito that instructions for subnetting could go on and on.

In the case of the OP network, supernetting the Class C by changing the subnet to 255.255.0.0, will allow him to use IP addresss 192.168.0.1 through 192.168.255.254 as usuable IP address, allowing 6553 IP address.

Usually the network is changed to a Class B network, using IP address 172.16.X.X, with subnet of 255.255.0.0, IP range of 172.16.0.1 to 172.16.255.254 allowing the same number of IP addresses and following the Subnet rules.

Hmmmmmm. You have two questions really, a technical question, and then a methodology question. I can answer the first one but the second one is all up for wild debate. Might as well be asking favorite colors

First we need to establish some references. An IP is made of a 32-bit integer commonly written as 4 8-bit integers in dotted notation. Each one of these 8-bit integers is referred to as a Class. So given that, an IP is A.B.C.D respectively to their class. The second thing is that everything is a binary representation. The short version is that everything is on a base-2 scale. For this reason, netmasks will always start with 0, 8, 16, etc. You will never have a netmask of 7.

A netmask in common form works as an inverse of your usable IP range. Each class (section) of an IP range consists of an 8-bit integer. The maximum value of this integer is 255 (256 digits, counting 0). What each section of a netmask is doing is providing a range within that class of the IP. The range is determined by subtracting the netmask number from the maximum number (256). For instance, if a part of the netmask is 255, that means the range is 1, or equal to the correlating section of the machine's IP.

So if we have '192' in our IP, and it's correlating section in the netmask is '255', that means the range is only 1 integer value, or '192'. Now if we have '192' in our IP, and it's correlating netmask section is '248', then we take 256-248=8. This gives us the range of our IP. So now we know we will have 8 IP's, and they will be in multiples of 8.

So now that we have a magic number of 8, we need to figure out exactly where our IP range starts and stops at. So you can spend a lot of time doing a math formula or you can just wing it like me. Basically when you wing it you are just doing multiples of 8 in your head until you find two neighboring multiples that include your IP. For instance, 8x24=192, and 8x25=200. Bingo, our IP is in a range of 192-199. The reason it's 199 is because 200 is the start of the NEXT range. If you do have a calculator, you can always divide your IP by your Multiple, and the whole-number part of the answer is the starting point of your range. For instance, 192/8=24, so I know my range is between 24th and 25th multiple of 8. If we pretend my IP was 194 instead, then we would get 194/8=24.25. We still get '24' as our starting point.

The 'data' and 'broadcast' IP's are always the first and last IP on your range. This is usually 0 and 255 with a full-class mask. In addition, the gateway is usually the first usable IP in your range.

So given that, here's some quick examples of those things applied:

Example: 192.168.200.0/255.255.248.0

A=192 (256-255=1 IP range)
B=168 (same as above)
C=200-207 (256-248=8, 200/8=25, 25x8=200, 26x8=208)
D=0-255 (any time you see 0 it means all IPs!)

Our usable range is 192.168.200.0-192.168.207.255.


Example: 67.153.177.49/255.255.255.192

A=67
B=153
C=177
D=0-63 (256-192=64, 49/64=0.7, 64x0=0, 64x1=64)

Our usable range is 67.153.177.0-67.153.177.63


I'll go over CIDR notation as well since it's being used quite a bit lately. All CIDR is is the raw bit form of the netmask. An IP consists of 32-bits. A netmask contains 32-bits. All CIDR is is the number of bits in a netmask that are 1 instead of 0. So the higher the CIDR, the smaller the range. So 255.255.255.248 = "/29" in CIDR form. The raw bits would contains 29 ones, and 3 zeros.

Just remember this is a binary mask and you are actually calculating the inverse of it. I usually just loosely do it in my head, knowing that every multiple of 8 = 255 in the netmask. So a /29 = 8+8+8+5. That means my netmask is going to be 255.255.255.X. To figure out X I take 5-8=3 (3-bits of IP range), so 2^3=8(binary to integer), then 256-8=248 (Remember, we are dealing with an inverse mask). That means my last part of the netmask is 248.

And for going the other way, we take 256-248=8. Then then solve 2^X=8, or 3. Then subtract 3 from 8 and end up with 5. So 248 from a netmask is a value of 5 in CIDR.

You can see more details of CIDR and netmask and how it all relates at wikipedia if you want: https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing#CIDR_blocks

The more VPN's you have, the more important supernet's or CIDR becomes. Lets say you have two offices, one with 100 computers, and one with 250. Office A is 192.168.10.0/24. Office B is 192.168.20.0/24. Without using CIDR, you could not add those 50 new stations to Office B without deploying routers to route traffic internally. That is assuming the solution is to only go from Class-C to Class-B netmask. I don't like that idea, as routers are just another point of complexity, failure, and bottleneck. For me, the solution is to change Office B from a /24 to a /23. That gives me 192.168.20.0-192.168.21.255. But while I was at it, I would probably just change it to a /22 or /21 and be done. I would then worry about changing subnets again when there were more then 768-computers in a single building network. And with the exception of routers, switches, and servers, you better believe I would be using DHCP so I wouldn't have to touch every machine in the process

But, that's just my opinion on it. Like I said in my other post, we might as well be debating our favorite colors. There is no clear right or wrong method

Thanks James for the very concise explanation. My head hurts. To all of those kids out there who never thought that math matters in school, think again. I can't tell you how many times that I wish I had paid more attention in Geometry class as well.

I was good at math, and I knew binary since before high school, (Many years ago) but still not great at figuring it out in my head. Good thing there are free calculators online.

Our office uses VLan with 2 192.168.xxx.xxx subnets. It works good 98% of the time, but it is the 2% that it doesn't that gets real annoying. I am definately a fan of making things simpler. I can VLan a network, but I would rather not if a VLan is not nessesary.

CIDR seems pretty convenient. I am wondering why they would drill classful routing into your head then say that none of it matters anymore. Maybe it is like most other tech out there, using an original method of IP addressing wil be 100% compatable with all devices but CIDR may not be?

Well, it is always good to get a grasp on the basics anyway. I still think it's funny when I see Token Ring or bus topology coax ethenet in these clases.

okay, its starting to make some sense, but barely...LOL.

Kumba, thanks for the clarification of counting backwards on the subnets.
So I understand that if there is a zero in the octet, then the entire range is open, if there are numbers in the octet, you would in essence count backwards to know how many IPs are open.

so in your example of using a subnet of 255.255.248.0 you come up with this..

A=192 (256-255=1 IP range)
B=168 (same as above)
C=200-207 (256-248=8, 200/8=25, 25x8=200, 26x8=208)
D=0-255 (any time you see 0 it means all IPs!)

Our usable range is 192.168.200.0-192.168.207.255.

then if the subnet mask is changed to 255.255.236.0, would my usable range now be 192.168.200.0 thru 192.168.215.255?? am I understanding this correctly?

When I had qwest, they gave me a range of public IP address, 8 to be exact. 71.33.253.0-71.33.253.7, With a subnet of 255.255.255.248
Am I to also assume that this was done solely to restrict my access to only the 8 IP addresses? Then they could assign 71.33.253.8-71.33.253.20 to someone else, and that person would have a subnet of 255.255.255.236? Is this correct?

Again, I appreciate this information. I am starting to gain some understanding of what is going on. A person with an IP address of 192.158.0.1 and subnet of 255.255.0.0 would have 256x256 addresses at theri desposal..that is a lot!!

And one more clarification. IP addresses and Subnets are binary numbers that are converted into xxx.xxx.xxx.xxx correct?

Actually 236 isn't representable as a binary value. So therefore the answer is non-existant.

The standard netmask definition is there to make things easy for people to read. It's a lot easier to do X-Y=Z in your head and know where things are at. It's however not really a good representation of what is actually going on under the hood. CIDR is the opposite. It's exactly how the computer understands it, but not the easiest for humans to read. Therein lies the conundrum.

The answer is that the next netmask after 248 is 240. Basically, the difference from netmask to netmask increases or decreases by a factor of 2 through 8 iterations. The reason there are 8 iterations is because each "class" has 8-bits assigned to it. This is referred to as a binary boundary. They are as follows (Remember, these are inverse mask, so subtract them from 256):

NM #-bits Math
---------------------------------
255 0-bits (2^0=1, so we get 255)
254 1-bits (2^1=2, 256-2=254)
252 2-bits (2^2=4, 256-4=252)
248 3-bits (2^3=8, 256-8=248)
240 4-bits (2^4=16, 256-16=240)
224 5-bits (2^5=32, 256-32=224)
192 6-bits (2^6=64, 256-64=192)
128 7-bits (2^7=128, 256-128=128)
0 8-bits (2^8=256, or all IPs in the range)

So, going from 248, which has 8 IP's in that range, to 240, would double your IP range to 16. Likewise, going from 248, to 252, would halve your IP range. A netmask will never be anything EXCEPT these values. After you see them enough you'll just memorize them like I have. Either that or you'll get good at exponentials in your head

And as far as your second question, yes. If CIDR wasn't utilized, Everyone would be on the same network, and you couldn't split up an IP range to multiple customers. Think of it like pie. Mmmmm, pieeeee. The class-based set-up represents a whole pie. The "bakery" has 256 of them. You have 2000 people who want pie. You don't have enough pie!

CIDR is essentially realizing that not everyone needs a whole pie. Mmmmm, pieeeee. So what you are going to do is take a knife and evenly cut the pies into sections so that way everyone can have a piece.

That's essentially all a netmask does. A way to subdivide an IP range so that it can be distinguished from others and separately routed. If your carrier only recognizes ip's in a .248, anything you try to do outside that won't work. Your network is LITERALLY defined as only being 8-IP's wide.


As far as your last question, essentially yes. A netmask is just a human-readable string of bits. For instance, the netmask 255.255.255.248 is actually:

11111111.11111111.1111111.11111000 (periods added for class reference)

In CIDR, you just count the number of one's and that is your /29. In netmask, you convert the bits into an integer by taking the number of one's as the power of 2. In this case the class-D would be 2^5 or 32.


As difficult as some of these concepts seem, they are a pale comparison to IPv6. There it's 8 groups of hexadecimal numbers. You will end up with IP Addresses that look like this:
2001:0db8:85a3:0000:0000:8a2e:0370:7334

Sounds fun huh? At least we will never have to change IP scheme again in anyone's foreseeable lifetime:
IPv4 - 4,300,000,000 addresses
IPv6 - 340,000,000,000,000,000,000,000,000,000,000,000,000 addresses

I forget the actual number, but I want to say that there was enough for their to be something like 1000 IPv6 addresses per every square inch on the face of the earth.

236 is not a valid number for a subnet. A subnet of 255.255.224.0 would give you a range of 192.168.192.1 to 192.168.223.254
There are only 9 different numbers you can use as a subnet number. 255, 254, 248, 240, 224, 192, 128, and 0.

"Restrict Access" is not realy correct. The ISP assign your range of IP address. Another customer could have the SAME subnet as you 255.255.255.248, and have the next range assignend to them XXX.XXX.XXX.9 through XXX.XXX.XXX.15 (8 and 16 would be unusable).
Again, 236 is not a valid subnet mask

The Subnet mask isn't to restrict access to another network, thats the firewalls job. The subnet masks tells your router or PC wheather the IP address you are trying to send information to is on your local network, or if they need to send the data to another router.


Everything with IPs and Subnets are binanary as far as the netork devices are concerned. They are shown in Decimal numbers so humans can read them easier.

The purpose of subnetting is not to restrict access but to more efficiently distribute IP addresses. Instead of assigning a 24 bit subnet where a customer will end up with 254 addresses of which they may only need 1 , they will subnet and assign a smaller group of addresses thereby conserving and better distributing the finite amount of available addresses. They may for example assign a 29 bit subnet such as 255.255.255.248 for 6 hosts.

You guys have provide a wealth of information here, and I am really begining to get a good feel out of this.

I am assuming the binary number representations are the same for all octets? In other words, if you have a subnet of 255.255.248.0, then the next possible usable subnet would be 255.255.240.0 correct?

And so to revist my original question, if I need 600 IP address, then I would need to have a subnet of 255.255.252.0

this would allow a range of 192.168.1.1 through 192.168.4.255. Did I do this math correctly?

Almost! The subnet 255.255.252.0
will allow up to 1022 IP addresses for hosts (network devices). Subnet mask of 255.255.254.0 will only allow 510. The only problem is the 1st usable IP is 192.168.0.1. You have to start the IP range from there. The IP 192.168.1.1 is within the 1st subnet.

The range of usable IP addresses in the 1st subnet with that subnet mask is 192.168.0.1 to 192.168.3.254. If you assigned a PC with 192.168.4.254 (you can't use the last IP address) then it could not talk directly to 192.168.1.1, because the PCs would think that they are on 2 different network subnets. They would need a router between them if they needed to communicate.


BTW, I have had a subnet calculator open for this entire thread. There are online and free ones you can use.

ahh...so the subnet does dictate what your starting IP address is. So you just cant throw in any range of addresses in the last octet. Rather in this case, since I have changed the value of the 3rd octet, I have to start at 192.168.0.1 and go up from there..

If I only needed less than 254 IP addresses, then I could basically us any private IP range that I wanted and it would not care since my subnet would be 255.255.255.0.

I am sure they make a subnet calculator for my iphone. I will have to look up one. I would always use one for sure, but at least now I understand a basic concept.

I think I have one last question. So I understand that only certain subnet numbers can be represented. Like Kumba said.. 255, 254, 252,248, etc... there is no binary value of 236, as I tried to use in my example. If IP addresses are binary, why are they not restricted as well?

As far a calcuators go, it is still important to know the math and how subnetting works. You could use it to check your work.

It sounds like you are taking a test of some type. I just recently took an online Adtran course, ATSA/IN. My other most recent cert, CTP, was getting about 3 years old.

The Adtran course goes through all this networking in an online slideshow type presentation. The second half is all about specific Adtran products. It is a free course and does not take very long. Like most network courses, online or classroom, you will have to practice subnetting.

You are starting to confuse represented data, like numbers and words and symbols that you and I read, for what a "mask" is.

To a computer, a "mask" is is a binary string to represent a pattern or grouping. They can also be called a bit-mask.

What you are thinking of is a "character set". What a character set does is define a translation path from binary strings to human-readable symbols like the words you are reading right now. For instance, in the ASCII character set (the standard for most lower-level systems), the value of 236 is represented as "001100100011001100110110". Morse code is also a good example of a binary character set.

They can also go by "Character Encoding", "Character Mapping", "Code Page", etc.

Hope that helps make sense.

Ohh, and as far as calculators go, I like to make use of this one when I feel lazy: https://www.subnet-calculator.com/cidr.php

Just to add to his point, any number can be converted to binary. Only a few numbers can represet a "mask". As Kumba pointed out, the binary value of 236 doesn't make a good mask, because it is full of holes.

The Class B mask
255.255.0.0 binary is:
11111111.11111111.00000000.00000000
<--------Network--|--Hosts---------->
Binary 1's represent the network
Binary 0's represent the hosts.

So is the 1st 2 Octets match, then they are on the same network. Within that network the HOSTS IP must be different.

On more example
255.255.240.0
11111111.11111111.11110000.00000000
1's and 0's are still together. No holes. A few more 0's in the subnet masks mean we have more IP addresses we can use for this network. The math gets a little fuzzier for mortals that don't work with binary every day, but for devices on the same network, the numbers in the Network part of the mask must be the same, and the Hosts must be different.

That is why only a few numbers can be used in the mask.

As Tito1411 said earlier in this thread:
"This is a very complex subject that I could spend days writing about"

"ahh...so the subnet does dictate what your starting IP address is. So you just cant throw in any range of addresses in the last octet. Rather in this case, since I have changed the value of the 3rd octet, I have to start at 192.168.0.1 and go up from there"

Just reread that. You dont HAVE to start at a number. I don't like 192.168.0.X because it is too common. Kumba mentioned this, the subnet is a pie slicer. Each slice is a fixed size depending on subnet mask. It has a fixed starting address and a fixed ending based on the mask. You could pick any IP within that range.

192.168.0.1/24 NOT on same network as 192.168.1.1/24
They will not even try to talk to each other directly.

but change subnet mask to 255.255.254.0:
192.168.0.1 CAN talk directly to
192.168.1.1
without a router because the PCs see each other as on the same network.

Am I overdoing it now? Sorry if I am clearifying something you already understand.

A subnet mask is a series of binary 1's followed by a series of binary 0's. The total number of binary digits in a subnet mask is 32. All the 1's must be on the left and all the zero's must be on the right. Here are all possible subnet masks:

00000000000000000000000000000000
10000000000000000000000000000000
11000000000000000000000000000000
11100000000000000000000000000000
11110000000000000000000000000000
11111000000000000000000000000000
11111100000000000000000000000000
11111110000000000000000000000000
11111111000000000000000000000000
11111111100000000000000000000000
11111111110000000000000000000000
11111111111000000000000000000000
11111111111100000000000000000000
11111111111110000000000000000000
11111111111111000000000000000000
11111111111111100000000000000000
11111111111111110000000000000000
11111111111111111100000000000000
11111111111111111110000000000000
11111111111111111111000000000000
11111111111111111111100000000000
11111111111111111111110000000000
11111111111111111111111000000000
11111111111111111111111100000000
11111111111111111111111110000000
11111111111111111111111111000000
11111111111111111111111111100000
11111111111111111111111111110000
11111111111111111111111111111000
11111111111111111111111111111100
11111111111111111111111111111110
11111111111111111111111111111111

an easier way to write the subnet mask is to just state the number of 1's it has. Using this notation, here are all possible subnet masks:

0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32

Write these down so you don't forget them.

An IP addresss can be followed by a slash and the number of 1's in the subnet mask. For example:

192.168.1.1/24 means an ip address of 192.168.1.1 with a subnet mask of 11111111111111111111111100000000.

Some people like to divide that string of ones and zeros up into four equal parts like this:

11111111.11111111.11111111.00000000

The dots here are not decimal points. They are just convenient dividing points in one big binary number.

Some people like to convert these four smaller parts of the number into decimal. So then they get:

255.255.255.0

because 11111111(binary) = 255(decimal)

But the subnet mask is not four numbers, it is still one big number.

The formula used to figure out the number of hosts within a subnet is:

h = m^2 - 2
where
h is the number of hosts (usuable addresses)
m is the number of bits used for the mask
the -2 is there because 2 addresses are not usable the first address of any network is the network number and the last address is the broadcast address.

Using the example 192.168.0.0 255.255.255.0
this can also be written as 192.168.0.0/24 where 24 is the number of bits that identifies the network (all the 1s)
m=8 because the mask uses 8 bits 11111111.11111111.11111111.00000000
h = 2^m - 2 becomes
h = 2^8 - 2 = 256 - 2 = 254
There would be 254 usable addresses with 192.168.0.0 reserved for the network address
192.168.0.1 - 192.168.0.254 for hosts and 192.168.0.255 reserved as the broadcast address.

192.168.0.0 255.255.254.0 or 192.168.0.0/23
11111111.11111111.11111110.00000000
m=9 so
h = 2^9 - 2 = 512 - 2 = 510
There would be 510 usable addresses with 192.168.0.0 reserved for the network address
192.168.0.1 - 192.168.1.254 for hosts and 192.168.1.255 reserved as the broadcast address.
Note that with this mask 192.168.0.255 and 192.168.1.0 are usable addresses.

Thanks again guys. While it might take me a long time to be an expert at this. All the information you guys have provided gives me enough information to at least understand the basic rules and principles of IP addresses and subnets. I also downloaded a couple of subnet calcs for my iphone and ipad.

I believe we might be able to put this topic to bed!!!

Thanks again guys!!

...
31
32

Other than for illustrative purposes you aint going to do much communicating on a /31 or /32 subnet.

And once you strip out the 0 and broadcast address, a /30 subnet really has room for only 2 devices!

For most regular business' you will usually get a /29 or /28. Only residential really gets anything smaller.

write the ip address in binary digits. Then underneath it write the subnet mask in binary digits too. Using 192.168.0.1 as an example:

11000000.10101000.00000000.00000001 =ip address
11111111.11111111.11111111.00000000 =subnet mask

now you can see that the binary 1's in the subnet mask are underneath the part of the ip address that is the number of the network. and the binary 0's are under the part of the ip address that is the number of the host.

So this is the network number: 11000000.10101000.00000000

and this is the host number:
00000001


That's all there is to it...

LOL, that's the short and sweet version alright. Only problem is that the people who can make sense of it in that form aren't the ones who need help figuring out what it means.

At least in IPv6 subnetting will almost never change for most end users considering everyone pretty much gets a /64 (LOL!).

Not clear? Each local area network (think small ofice suite) has a network number and each computer has a computer number. Two computers that have the same network number are on the same network, and two computers that have different network numbers are on different networks.

If a computer knows:

1. it's own ip address
2. another computer's ip address, and
3. it's own subnet mask, it can figure out whether or not both computers are on the same local area network.

Yes, I understand it. What I was trying to say is that most people need to be warmed up to the whole topic before you can just throw binary at them. Your explanation requires a lot of ancillary knowledge that you are taking for granted.

kumba you have dashed my hopes to become a technical instructor!

Let me try it this way. Each house has a number and each street has a name. If you are on the same street as another house, it is probably in your local area. How is that?

I was getting around to the idea that if two computers are on the same local area network (think cable) then they can talk directly to each other. Think of it as working in the same room as someone else. You can just shout across the room.

However if two computers are on different local area networks, then they need a go-between computer to communicate. This go-between computer is connected to both local area networks and passes messages from one LAN to another. Think of it as a secretary who sits in the doorway between two rooms. If you want to talk to someone in the next room, you shout her the message, and she shouts it to the person in the next room.

Can anyone tell me what we call this go-between?

Your fired!

Way too simplistic and vague. That explanation does not even come close to explaining how a subnet mask and ip address work together which was the original question.

The 1st explination said what a Subnet did, but the binary part may be where I can see where question marks start shooting out from some people's head. Throw out a bit of AND, OR, NOT Boolean to make the rest of the follows dizzy.

I like the stream of 1's and 0's on the earlier port, While it doesn't explain what a subnet mask is, it does visualize why only some numbers can be a subnet mask (related to the question at the time). It still requires some understanding of what binary is and how it relates to the numbers people see as it relates to IP, altho that was also explained in the same post.

If someone read all these posts and still don't knbow what a subnet does, then I am not sure of a better way to explain it.

Maybe instead of a secretary (router) it was a mail runner guy for a corporate offce.

Letter for Bob. His office number is 192.168.0.100.
The mail guy is at office 192.168.5.20. He looks at the subnet sign on the wall. Hmm, it says 255.255.255.0.
All the 255s = XXX, The 0's = OOO
192.168.000.100
XXX.XXX.XXX.OOO
192.168.005.20
XXXs have to match.
The 005 does not match 000, so mail runner knows Bob is not at this building. He will give the letter guy in the mail truck. He will send it to the correct building where Bob is located.


Well, that was the best I could come up with. I know that it does not explain subnetting with numbers other then 255, which was also part of the original qustion.

What does a subnet mask do? It tells the computer how much of its ip address reprsents the network it is on and how much of its ip address represents its number on the local area network.

How does it do that? I think that was explained above. But think of it as a mask put over the ip address. If you look thru the zeros in the network mask, you see your host number. If you look thru the ones, you see your network number.

Whoever invented IP decided that ip addresses would be fixed in length but that some local area networks could be larger than others.

By the way, the subnet mask is set on the computer but NEVER transmitted to another computer. A potent source of misconfiguration!

There are only 10 kinds of people. Those who know binary and those who don't.

I like that one. :rofl:
I have seen it before, but it I still like it.