IP Security (IPSec)
IPSec has become the standard for cryptographic services IP level, offering confidentiality, integrity and authetication of extremes. The standard is mandatory for IPv6 solutions, for which it is defined, and has been adapted solutions for IPv4, the which is otional.
The main concept is to define IPSec Security Association (SA). A SA represents a logical connection between two entities unidirectional IPSec, and offers services traffic safety held by them. These security services are provided by two headers that are added to standard IP: AH (Authentication Header) and ESP (Encapsulating Security Payload). The first offers integrity in the connections, origin authentication and optional anti-forwarding service. The second is more complete and the services offered by AH offers confidentiality. VPN uses ESP.
The implementation has been used KLIPS IPSec (IP Security Kernel) included in the software FreeS / WAN. This solution enables secure networks no tunnels reliable IP packets being routed between any separate SGs network topology.
The result is a virtual IP connection that allows us to define our VPN.