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How to check if 2 IP Addresses fall in the same subnet ?

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donchen    9

How do I check if the 2 IP addresses are in the same subnet ?

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+BudMan    3,720

You would look at the mask..

Please post both IPs an the mask for each.

Ie 192.168.1.14 mask 255.255.255.0 would be on the same network as 192.168.1.128 mask 255.255.255.0

But if the mask was 255.255.255.128 then they would not.. the last host of the first subnet would be .126

If the mask was only 255.255.0.0 then 192.168.1.? and 192.168.254.? would be on the same network.

http://en.wikipedia.org/wiki/Subnetting

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donchen    9

137.157.7.65

137.157.10.3

mask = 255.255.252.0

I believe that they are NOT in the same subnet right ? But what is the shortest explaination for it ?

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k22    5
137.157.7.65

137.157.10.3

mask = 255.255.252.0

I believe that they are NOT in the same subnet right ? But what is the shortest explaination for it ?

i'm still learning myself, but this is what i come up with

137 is Class B, so the first 2 octets are always the same (137.157)

because the mask is a /22, the networks are increasing by 4 each time

137.157.0.0			 137.157.0.1 - 137.157.3.254			 137.157.3.255
137.157.4.0			 137.157.4.1 - 137.157.7.254			 137.157.7.255	(1st address is a host address)
137.157.8.0			 137.157.8.1 - 137.157.11.254		   137.157.11.255 (2nd address is a host address)

therefore they are on 2 different subnets

you can use a subnet calculator to verify

http://www.subnet-calculator.com/subnet.php?net_class=B

http://www.subnetmask.info/

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Sparky101    13

That is correct, they are in different subnets.

The way to work this out involves converting the IP address to binary, then applying the subnet mask to work out the network address for each IP address. If the network address is the same they're in the same subnet, if not they aren't. Using the addresses you posted this works out as follows:

137.157.7.65 in binary = 10001001 . 10011101 . 00000111 . 01000001

255.255.252.0 in binary = 11111111 . 11111111 . 11111100 . 00000000

Network address = 10001001 . 10011101 . 00000100 . 00000000 (Network address is worked out by copying the 1's and 0's from the IP address where the subnet mask has a 1 and then putting a 0 in where the subnet mask has a 0)

Therefore network address is 137.157.4.0. Do the same for the other address and you get 137.157.8.0. Therefore different subnets. There's a useful tool on the Boson website, called Subnet Calculator which works this stuff out automatically.

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donchen    9

Is there anyway I can route a packets to a private address ? What are such technologies call ?

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+BudMan    3,720

So what do we get for doing your homework? ;)

Network Address Translation (NAT) is the term your looking.

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donchen    9

I wrote NAT but they said what technologIES ?

So i presume there is more that NAT ?

Lol, come'on Budman, just lending a poor student some helping hand =P

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+BudMan    3,720

Well you would forward traffic from the outside of a nat to the inside. Port Forwarding..

There are different types of NAT, what most home routers use is really NAPT or PAT.. port address translation in sharing 1 public IP address with many private ones.

It can also be called IP Masquerading, or Network Masquerading if that is the other term they are looking for?

As to the technologies -- routing would be required as well ;) An IP address is an IP address, there is nothing that keeps you from routing traffic anywhere you want.. As long as the routers in between know where to go next, etc. The problem is -- router on the net do not route private addresses, kind of what makes up private ;) An could not, since they are used in more than 1 place, etc. ;)

But on a isolated network there is nothing that stops you from routing a public IP address to a private one, etc.

Maybe if you did your coursework you would not need to ask others to do your homework for you ;)

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