vether —
virtual Ethernet interface
The vether interface simulates a normal Ethernet
  interface by encapsulating standard network frames with an Ethernet header,
  specifically for use as a member in a
  bridge(4).
To use vether the administrator needs to
    configure an address onto the interface so that packets can be routed to it.
    An Ethernet header will be prepended and, if the
    vether interface is a member of a
    bridge(4), the frame will show
    up there.
The vether interface first appeared in
  OpenBSD 4.7 and NetBSD 10.
Like tap(4), the Ethernet address
  chosen will be partially random, and may occasionally collide with another
  address.