Router from the outside

[unfalliblekrutch]

Essentially, the question is, can an ISP tell the difference between a computer directly connected to a modem versus two or more computers connected to a router if the router assumes the same MAC address as the original computer? If so, how?

This is mostly out of curiousity. I always thought no, but someone else has tried to tell me yes.

 

[skyking]

Yes. An extra bit gets set on packets so your router can send the information to the proper computer on the inside. Do they care? Usually not.

 

[Nuwave]

This is the first time i've ever heard of an 'extra bit' If that's the case then a router will only be able to keep track of 2 computers, 0 or 1.

In the case of a typical home router, which uses NAT (Network Address Translation), the router will keep track of what goes out to the wan in a table based on source port and destination address from the internal LAN. When a responce is recieved from the internet the router looks at the Destenation port and source address and if there is a match pass the packet along to the appropiate machine. This method accomodates as many computers/connections as the memory can process.

I'm trying to think of a way someone could effectively determine the number of computers behind a router, but I just can't if you I only see the outside of the router.

 

[unfalliblekrutch]

Well, I hear something about how a computer would use ports incrementally while a router assigns them randomly or maybe it was the other way around. So, if the ISP sees ports being used incrementally, it's most likely one and if ports are used randomly, it's most likely the other

 

[Nuwave]

Programing in the application will use either static, icremental or random source ports. Destination ports are almost always a static port. Eitherway networking equipment make decisions based on the ports, sometimes modifying them in the case of PAT, but they don't assign port numbers.

 

[JackMDS]

These days this is really a mute issue.

Main Stream ISPs give clients a Router, and there is No stipulation about the number of computers.

In any case if an ISP makes it his business to find out about multicomputer behind a Router all they have to do is to Intercept the stream for a while.

When used, the pattern of a single computer's stream looks differently than a multicomputers.

 

[Modelworks]

Could they tell if they really wanted to ?
Yes

Are they going to dedicate the time needed ?
No

 

[n0cmonkey]

Incremental source port allocation is a bug. Bad juju. Avoid those systems.

And yes, it's possible. Just not usually worth the effort.

 

[1LordEmperor1]

Your ISP doesn't really care if you have multiple computers.

They MIGHT care if you pulled down more than your allocated number of public IP addresses, but your router solves that problem.