SSL VPN principles

SSL VPNs enable remote access to intranet resources (an entity's private network) either from another intranet, or from isolated equipment, by simulating HTTPS requests. Resources can be servers (Web applications, file sharing, Telnet access, etc.) or IP subnets. Using HTTPS is transparent to existing infrastructures (figure 1 ):

• Firewalls are generally configured to allow outgoing TCP flows on port 443 ;

• NAPTs (Network Address Port Translation) let outgoing TCP flows pass through them without any problem. NAPTs are designed to convert a set of source addresses into a single source address: all machines on a private network are seen as a single machine;

• proxy servers (or Web proxies)...