1.21 IPsec

CCNP RS 300-101, Describing Routing Protocols, Uncategorized

IPsec is a suite of protocols that is widely used to securely connect remote offices and remote users. It provides the following capabilities.

  • Confidentiality: Encryption
  • Data Integrity: Use of checksums ensure the payload has not been altered
  • Authentication: Certifies the sender and recipient of the communication
  • Anti-Replay: Verifies each packet is unique to thwart attempts to bypass security

Internet Key Exchange (IKE) is used to ensure authentication. It uses username/password, one-time passwords, pre-shared keys (PSKs), and digital certificates for this purpose.

Regarding anti-replay protection, IPsec assigns an increasing sequence number to each individual packet, and those sequence number are compared to a sliding window on the receiving host. If a packet arrives with a sequence number less than the number of the window, it is considered duplicate or late, and is dropped.

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