Send a request to get an external IP from an active IP address

[npavel]

Please make it so that server tried to get external IP address by sending request from that IP address to which the client connects.

It needed to implement the following scheme with multiple gateways:

            / [gateway 1, wan ip: 1.1.1.1, lan ip: 192.168.1.1] \
[ftp client]                                                     [ftp server]
            \ [gateway 2, wan ip: 2.2.2.2, lan ip: 192.168.2.1] /

I have a two IP addresses and default gateways on a single ethernet interface (although it may be different interfaces too):

1. ip: 192.168.1.2/24, dg: 192.168.1.1, metric: 10
2. ip: 192.168.2.2/24, dg: 192.168.2.1, metric: 20

FileZilla Server listens to both of these addresses, is configured to passive mode and gets an external IP address from ​http://ip.filezilla-project.org/ip.php.

At the moment FileZilla Server always connect to ip.filezilla-project.org from 192.168.1.2.