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Re: PHP socket and NAT [message #177127 is a reply to message #177122]

Thu, 23 February 2012 13:04

SL
Messages: 20
Registered: February 2012

Karma:

Junior Member

>> NAT typically is used to change IP-addresses (and maybe port).
>> If A and B are in the same LAN I expect they can address each other
>> directly.
>> For example:
>> A IP: 192.168.178.22
>> B IP: 192.168.178.25
>>
>> Once you go outside your LAN, you (might) need NAT.
>>
>> And sockets have little to do with NAT.
>> A IP package arrives at a certain IP on a certain port: If some
>> socket is listening on that port on that machine, the package will
>> be handled by the listening process.
>>
>> NAT itself is performed by routers and such, not by some service
>> listening to a port.
>>
>> SO in short: No you have to care about it.
>>
>> Disclaimer: If you are talking IP6, things are different.
>>
>> Regards,
>> Erwin Moller
>>
>
> An additional example of NAT that makes things clear.
> This is how it was explained to me when I wanted to know about NAT.
>
> Suppose you have 10 computers on your LAN, and 1 internet gateway
> (some ADSL modem for example).
> All you 10 computers can connect to the internet because they use the
> routers IP address as the gateway.
>
> The router has an INTERNAL (LAN-side) IP address.
> Let's say this LAN-IP is 192.168.178.1
>
> The router also has an EXTERNAL (Internet-side) IP address.
> Let's say internet-side IP is 69.147.94.94. (I made the numbers up)
>
> Now, suppose a few people on the LAN are visiting some websites.
> Suppose compA has IP address 192.168.178.22. (On the LAN)
> Suppose compA has IP address 192.168.178.50. (On the LAN)
>
> CompA (192.168.178.22): requests www.google.com
> CompB: (192.168.178.50)requests www.php.net
>
> The router receives these requests from the LAN side, and sends the
> requests to www.google.com and www.php.net.
> The servers from Google and PHP answer the requests, and send them
> back to the router's IP address (being 69.147.94.94).
>
> Now the problem: How should the router handle these answers? Should it
> send them to 192.168.178.22 or 192.168.178.50, or even another IP on
> the LAN?
>
> This is where NAT comes into the picture.
> It works like this:
> 1) Router receives request from 192.168.178.22 (=LAN)for
> www.google.com. 2) Router thinks up some random port that is not is
> use, eg 33000. 3) Router stores this portnumber (33000) in a table
> together with the requesting LAN IP-address (192.168.178.22).
> 4) Router sends the request to www.google.com TOGETHER with the
> instruction to answer on port 33000.
> 5) When Google answers, the router looks up the portnumber, ans sees
> what (internal) IP-address made this request. This way the router can
> see which internal IP-adress made what request because they all get
> random assigned portnumbers.
>
> That is NAT in short.
>
> So I don't expect you have to worry about that in your case.
>

This example clears the air. So the key is the router comes up with random
port number, and the reply specifies that port number.

Thanks a lot.

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[Message index]

		PHP socket and NAT By: SL on Thu, 23 February 2012 08:58
		Re: PHP socket and NAT By: Erwin Moller on Thu, 23 February 2012 10:32
		Re: PHP socket and NAT By: Captain Paralytic on Thu, 23 February 2012 10:41
		Re: PHP socket and NAT By: Erwin Moller on Thu, 23 February 2012 10:53
		Re: PHP socket and NAT By: Erwin Moller on Thu, 23 February 2012 10:52
		Re: PHP socket and NAT By: SL on Thu, 23 February 2012 13:04
		Re: PHP socket and NAT By: The Natural Philosoph on Thu, 23 February 2012 13:37
		Re: PHP socket and NAT By: The Natural Philosoph on Thu, 23 February 2012 11:40
		Re: PHP socket and NAT By: Jerry Stuckle on Thu, 23 February 2012 13:00
		Re: PHP socket and NAT By: SL on Thu, 23 February 2012 13:09
		Re: PHP socket and NAT By: Captain Paralytic on Thu, 23 February 2012 13:19
		Re: PHP socket and NAT By: The Natural Philosoph on Thu, 23 February 2012 13:53
		Re: PHP socket and NAT By: Captain Paralytic on Thu, 23 February 2012 14:25
		Re: PHP socket and NAT By: Michael Fesser on Thu, 23 February 2012 17:28
		Re: PHP socket and NAT By: The Natural Philosoph on Thu, 23 February 2012 20:42
		Re: PHP socket and NAT By: M. Strobel on Fri, 24 February 2012 10:58
		Re: PHP socket and NAT By: SL on Thu, 23 February 2012 16:03
		Re: PHP socket and NAT By: The Natural Philosoph on Thu, 23 February 2012 20:44
		Re: PHP socket and NAT By: M. Strobel on Fri, 24 February 2012 11:07
		Re: PHP socket and NAT By: The Natural Philosoph on Fri, 24 February 2012 13:22
		Re: PHP socket and NAT By: Tim Streater on Fri, 24 February 2012 14:20
		Re: PHP socket and NAT By: The Natural Philosoph on Fri, 24 February 2012 15:39
		Re: PHP socket and NAT By: Tim Streater on Fri, 24 February 2012 18:53
		Re: PHP socket and NAT By: The Natural Philosoph on Fri, 24 February 2012 21:04
		Re: PHP socket and NAT By: Tim Streater on Fri, 24 February 2012 21:41
		Re: PHP socket and NAT By: Peter H. Coffin on Sun, 26 February 2012 18:50
		Re: PHP socket and NAT By: Erwin Moller on Thu, 23 February 2012 13:37
		Re: PHP socket and NAT By: The Natural Philosoph on Thu, 23 February 2012 13:50

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