Mohit Anchlia wrote:
You are perfectly right : the router knows the real IP address. But it will not tell you, haha.On 6/4/08, Dragon <dragon@xxxxxxxxxxxxxxxxxx> wrote:André Warnier wrote: Mohit Anchlia wrote:2. Another question I had was sometimes we don't get real physical IP ofthe machine but the IP of something that's in between like "router", is there a way to get the real IP so that we don't end up blocking people coming from that "router" or "proxy"In my opinion, you cannot. The whole point of such routers and proxies is to make the requests look like they are coming from the router/proxy, so that is the sender IP address you are seeing at your server level, and that's it. Your server never receives the original requester IP address.---------------- End original message. --------------------- There are legitimate reasons for this to be done as well, indiscriminately blocking such access is a bad idea as it will affect legitimate users. NAT and IP address sharing are among the reasons. This allows an organization to have a router with one public IP address to serve a larger internal network with private IP addresses. Without this, we would have run out of IPv4 addresses a long time ago. DragonIf there is no way to get the real IP address then how would router know which machine to direct the response to. It got to have some information in the packet. For eg: If A send to router B and router sends to C then when C responds how would B know that the response is for A.
Seriously, this is how it works :the original system sends out an "open session" packet, through the router, to the final destination. The router sees this packet, and analyses it. It extracts the IP address and port of the original sender, and keeps it in a table. Then it replaces the IP address by it's own, adds some port number, and also memorises this new port number in the same table entry.
Then it sends the modified packet to the external server (yours).It knows that the server on the other side is going to respond to this same IP address and port (the ones of the router). When the return packet from the server comes back, the router looks at the port in it, finds the corresponding entry in it's table, and now it knows to whom it should send the packet internally.
And so on. So : - the router knows everything - the internal system thinks it is talking directly to the external server- the external server (yours) only sees the router IP and port, so it thinks that is where the packet comes from.
That's NAT for you, in a nutshell. Yes ? --------------------------------------------------------------------- The official User-To-User support forum of the Apache HTTP Server Project. See <URL:http://httpd.apache.org/userslist.html> for more info. To unsubscribe, e-mail: users-unsubscribe@xxxxxxxxxxxxxxxx " from the digest: users-digest-unsubscribe@xxxxxxxxxxxxxxxx For additional commands, e-mail: users-help@xxxxxxxxxxxxxxxx
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