Provide access through single IP

Question

I've assigned a dedicated IP on my server to one of my customer via Plesk. But when he accesses any external content the IP reflected there as Host IP is the primary one of my server and not the dedicated one that is assigned to him. What could be the problem and how will I solve this.

Answer 1

The dafault behaviour in all TCP/IP stacks is that unless you specify otherwise, outgoing connections bind to the first address on the outgoing interface for the route the connection needs to take (and if there are two interfaces through which the connectino could be routed, the first in the routing table will be picked) - in this case your primary address. If you need to appear to come from one of the other addresses, or need/want to force the choice of interface the connection is routed through you need to specify the local interface or address to bind to.

Many libraries and tools expose this option, for instance cURL with it's --interface option:

curl --interface 192.168.1.10 http://www.example.com/document.html
curl --interface eth2 http://www.example.com/document.html
curl --interface eth0:1 http://www.example.com/document.html

which is exposed by most language bindings for libcurl, such as in PHP:

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "http://www.example.com/");
curl_setopt($ch, CURLOPT_INTERFACE, "192.168.1.10");
curl_exec($ch);
curl_close($ch);

^{[I chose cURL as an example as it is a very common method used for conncetions to external services, and you gave no indication in your question as to what external connections were a problem. Other libraries and tools usually offer similar options - check their documentation for details]}

This is not something you can do as an administrator: your user needs to update his code to control which interface/address his outgoing connections bind to rather than just allowing the IP stack to follow its default behaviour in that respect.