A bridge domain is a generic broadcast domain that is not tied to a specific transport technology. Bridge domains support a wide range of service endpoints including regular L2 endpoints and L2 endpoints over L3 technologies.
Bridge domains switch packets between a range of different endpoint types; for example, attachment circuit (AC) endpoints, Virtual Private LAN Service (VPLS) endpoints, Virtual Leased Line (VLL) endpoints, and tunnel endpoints.
A bridge domain that is created for a VPLS application is also referred to as a VPLS instance.