Helper router is enabled under VRRP per VRID per VLAN interface on access SPB switches
that ingress to customer VLANs in an RaaS context. Helper router route tables confine routes to
connected VLAN interfaces where an interface represents a customer VLAN. The Helper router
learns the identity of Main routers by the propagation of type 250 TLV through the SPB network by IS?IS.
Helper routers redirect unresolved destination networks to the Main routers.
The Main router responds to ARP requests for any virtual IP address and sends VRRP
advertisements to ensure the virtual MAC remains in bridge FDBs within the SPB domain. Helper
routers install the VRRP virtual MAC address into the local filter database for packet processing
by the forwarding plane.