Typically, in a VPLS environment over MPLS, mesh and spoke-SDP binds interconnect the local VPLS instances to remote PEs. To support VPLS E-Tree, the root and leaf traffic is sent over the SDP bind using a fixed VLAN tag value. The SR OS implementation uses a fixed VLAN ID 1 for root and fixed VLAN ID 2 for leaf. The root and leaf tags are considered a global value and signaling is not supported. The vc-type on root-leaf-tag SDP binds must be VLAN. The vlan-vc-tag command is blocked in root-leaf-tag SDP-binds.
Figure 1 shows the behavior when leaf-ac or root-ac interfaces exchange traffic over a root-leaf-tag SDP-binding.
Figure 1. Leaf and Root Tagging PW
