Also informally known as CIP. An IETF specification for transmitting IP datagrams and ATM Address Resolution Protocol (ATMARP) requests and replies over ATM Adaptation Layer 5 (AAL5) where ATM is configured as to include multiple logical IP subnetworks (LISs).In Classical IP over ATM, ATM replaces a legacy local area network (LAN) such as Ethernet.The term classical derives from the fact that IP packets between two logical subnets on the same ATM network must go through an intervening router. Subsequently, alternative methods were defined for transmitting IP datagrams over ATM networks, with those methods including LAN Emulation (LANE), and Multiprotocol over ATM (MPOA). Classical IP over ATM was originally defined in IETF RFC 1577 (1994) and most recently in IETF RFC 2225 (1998). See also AAL5, ARP, ATM, datagram, IETF, IP, LANE, MPOA, and subnet.