How does ASP obtain the real IP address of the client?

Use request. servervariables ("remote_addr") to obtain the IP address of the client, but if the client is accessed by the proxy server, the obtained IP address is the IP address of the proxy server, not the real IP address of the client. To obtain the real IP address of the client through the proxy server, use request. servervariables ("http_x_forwarded_for") to read. However, not every proxy server can use request. servervariables ("http_x_forwarded_for") to read the real IP address of the client, some of which are still the IP address of the proxy server. Note that if the client is not accessed through the proxy server, the value obtained using request. servervariables ("http_x_forwarded_for") will be null. Therefore, if you want to use this method in the program, you can do this:
......
Userip = request. servervariables ("http_x_forwarded_for ")
If userip = "" Then userip = request. servervariables ("remote_addr ")
......

That is, if the client uses the proxy server, the value of http_x_forwarded_for is obtained. If the client does not pass the proxy server, the value of remote_addr is obtained.

'Common function: if the real IP address of the client cannot be obtained, the proxy IP address of the client is obtained.
Private function getip ()
Dim stripaddr
If request. servervariables ("http_x_forwarded_for") = "" Or instr (request. servervariables ("http_x_forwarded_for"), "unknown")> 0 then
Stripaddr = request. servervariables ("remote_addr ")
Elseif instr (request. servervariables ("http_x_forwarded_for"), ",")> 0 then
Stripaddr = mid (request. servervariables ("http_x_forwarded_for"), 1, instr (request. servervariables ("http_x_forwarded_for"), ",")-1)
Elseif instr (request. servervariables ("http_x_forwarded_for"), ";")> 0 then
Stripaddr = mid (request. servervariables ("http_x_forwarded_for"), 1, instr (request. servervariables ("http_x_forwarded_for"), ";")-1)
Else
Stripaddr = request. servervariables ("http_x_forwarded_for ")
End if
Getip = trim (mid (stripaddr, 1, 30 ))
End Function

Add another sentence:
Request. servervariables ("remote_addr") & "<br>" 'to obtain the Client IP Address
Request. servervariables ("local_addr") & "<br>" 'to obtain the Server IP Address

From: http://hi.baidu.com/etong168/blog/item/7439469011cd3c8da877a46c.html