A secure client-server connection based on a trusted certificate is the main prerequisite for any VPN service based on the IPSec specification.

The process of creating this link is so important that it has its very own name – Security Association, or SA. Yes, that’s a capital “A” and an abbreviation, so it essentially has a last name as well with initials to top it off – that’s how essential it is to the very concept of IPSec and security based thereon.

There are three components to SA – a security protocol ID, destination IP address, and a security parameter index (SPI). The protocol ID is a number that refers to either an Encapsulated Security Payload (ESP) or the Authentication Header (AH), i.e. it’s the number 50 and 51, respectively.

The SPI is how the SA (remember what those two mean?) is authenticated, being a 32-bit value generated following a unique SA identification. It bears pointing out that a single successfully completed SA means nothing without a counterpart because the entire process described above is unidirectional, i.e. it only goes one way.

Similar questions to “Before ipsec can be used as a virtual private network (vpn) service, what must be created?”:

We also answered these questions, do check them out:

  1. What dedicated hardware device aggregates hundreds or thousands of vpn connections?
  2. Which VPN protocol uses UDP Port 1701 and does not provide confidentiality and authentication?
  3. Which process is used to protect transmitted data in a VPN?
  4. When employees have multiple concurrent connections, what might be happening to the VPN system?
  5. What does a VPN use to ensure that any transmissions that are intercepted will be indecipherable?
  6. Which VPN protocol works at Layer 3 and can encrypt the entire TCP/IP packet?