Data link switching (DLSw) is a tunneling protocol used to direct unroutable non-IP protocols across IP networks.
These protocols include unroutable and non-IP-based protocols like the IBM Systems Network Architecture (SNA) or NetBIOS Frames (NBF).
DLSw is a way of transporting SNA and network basic input/output system (NetBIOS) traffic through an IP network. DLSw serves as an alternative to source-route bridging and carries local area network traffic over a wide area network by first encapsulating the traffic in TCP packets.
DLSw was first made available to the public in 1993 as IETF RFC 1434. It was further enhanced and republished in 1995 as IETF RFC 1795. DLSw was jointly developed by the Data-Link Switching Related Interest Group and the Advanced Peer-to-Peer Networking Implementors Workshop.
The three primary functions of DLSw are:
1. Mapping of local data-link control (DLC) connections to a DLSw circuit
2 Terminating SNA DLC connections to help to reduce the chances of link-layer timeouts across WANs
3. Maintaining the Switch-to-Switch Protocol (SSP) between two DLSw routers or nodes
Data link switching was originally created by IBM to add SNA support in multiprotocol routers and transport SNA and LAN traffic over a WAN by encapsulating the data in TCP packets.DLSw routers are called peers and the connections between them are called peer connections. DLSw works by establishing two TCP connections between two participating peers. The two peers then exchange capabilities such as DLSw version numbers, which are NetBIOS names known media access control addresses. There are three types of peers:
Active Peer: This peer establishes connections with other known peers.
Passive Peer: This peer accepts connections from other known peers.
Promiscuous Peer: This peer accepts any connection from any peer, whether known or not.