Alcatel-Lucent 7750 SR Manual page 579

Virtual Private LAN Services
It is important understand the significance of the split-horizon-group used by the pw-template.
Traditionally, when a VPLS instance was manually created using mesh-sdp bindings, these were
automatically placed in a common split-horizon-group to prevent forwarding between the
pseudowire in the VPLS instances. This prevents loops that would have otherwise occurred in the
Layer 2 service. When automatically discovering VPLS service using BGP AD the service
provider has the option of associating the auto-discovered pseudowire with a split-horizon group
to control the forwarding between pseudowires.
7750 SR OS Services Guide Page 579