http://www.rfc-editor.org/rfc/rfc6054.txt
RFC 6054: Using Counter Modes with Encapsulating Security Payload (ESP) and Authentication Header (AH) to Protect Group Traffic, D. McGrew, B. Weis2010-11-01T23:00:00-00:00Counter modes have been defined for block ciphers such as the Advanced Encryption Standard (AES). Counter modes use a counter, which is typically assumed to be incremented by a single sender. This memo describes the use of counter modes when applied to the Encapsulating Security Payload (ESP) and Authentication Header (AH) in multiple-sender group applications. [STANDARDS-TRACK]