A virtual private network (VPN) is a technology that builds an encrypted tunnel across an untrusted network, letting two endpoints communicate as though they shared a private link. A remote employee uses one to reach corporate systems safely over home or hotel internet, and a site to site VPN connects two office networks over the public internet without exposing that traffic in the clear.
Common protocols include IPsec, which operates at the network layer and suits site to site links, SSL and TLS VPNs, which run at the application layer and are popular for remote access, and WireGuard, a newer and lighter design. One decision the exam likes is split tunneling versus full tunneling. Split tunneling sends only corporate traffic through the VPN, which is faster but skips your inspection controls for everything else, a quiet security tradeoff many organizations get wrong.
Why does a VPN matter for the CISSP exam?
VPNs live in Domain 4: Communication and Network Security, worth 13 percent of the exam. Know IPsec tunnel versus transport mode, split versus full tunneling, and how a VPN protects the confidentiality and integrity of data in transit.