tcp address 1

[neoice]

hello,


Can somebody explain what the purpose of a subnet mask is.

I understand that class A is 1-127.h.h.h 255.0.0.0

B is 128-191.n.h.h 255.255.0.0
C is 192-223.n.n.h 255.255.255.0

I am confused because at work our IP is class C with what looks like a class A submask.

192.168.0.x 255.0.0.0

So why isn't the submask 255.255.255.0

There are maybe 100 computers at work.

The IT guy doesn't like telling us anything at work. He says its to complicated to explain.

thanks

neil

 

[jimbopalmer]

I invite corrections and amplifications but this is my understnding:

The subnet mask decides how much of the address in on your side of the router, and how much is on the other side of the router.

in you example
with a subnet mask of 255.0.0.0 it will decide all of 192.x.x.x is local to your network, and any address that does NOT start 192.x.x.x is remote to your network. (This is almost undoubtabiliy wrong, as you should not own all of 192.x.x.x Your user cannot get to sites outside your company that start 192.x.x.x)

if your subnet mask was 255.255.0.0, in your example then all of 192.168.x.x would be local to your site, and everything outside of 192.168.x.x (While purists would still claim this is wrong, this would not actually foul you up in practice as all of 192.168.x.x is reserved for private networks)


The 255.255.255.0 subnetmack is best for you site unless the IT guy has used multiple third octets (192.168.0.x and 192.168.1.x as examples) without dividing them into subnets. I tried to remain child-like, all I acheived was childish.

 

[jono261970]

hello,

Thanks for your help. this is what i thought. I have only just started to learn TCP/IP so I wasn't sure. All computers are 192.168.0.x and 255.0.0.0 because I compiled a list to help me with my studies.

The proxy server is on 192.168.0.5 and I believe it has a second NIC in it with a public IP on which goes to the router.

cheers,

neil

A good fortune may forbode a bad luck, which may in turn disguise a good fortune.

 

[nokiakid]

In theory the addressing scheme is wrong, but I disagree that it is going to cause any problems like not being able to access outside websites that start with 192.x.x.x. Most ISP's and routers provide NAT so your IP will be changed and not be visible to the outside world.

change it to 255.255.255.0 for the purists.

 

[Accessdabbler]

Ya, I agree the subnet mask should be set to 255.255.255.0. The IT guy may have set up the proxy server to do some magical things to allow you to access addresses that start with 192.1-167.x.x or 192.196-255.x.x but I can't see the reasoning for this.

My experience has shown that when something is too complicated to explain, the explainer probably doesn't understand it either. They certainly don't want you to find out they don't know.

 

[jimbopalmer]

Help me with this, if my subnet mask is 255.0.0.0 and I am at 192.168.1.99 and I want send a packet to 192.152.176.77, won't my PC try to get there directly and never send the packet to the router? (I do see that if it ever went to the router, NAT would solve the problem) I tried to remain child-like, all I acheived was childish.