Best Practice: The logical interfaces in a VPLS routing instance may have the same or different VLAN configurations. VLAN normalization is required to switch packets correctly among these interfaces. VLAN normalization is effectively VLAN translation wherein the VLAN tags of the received packet need to be translated if they are different than the normalized VLAN tags. Configuration is described starting in IEEE 802.1ag OAM Connectivity Fault Management Overview and you should further observe the additional requirements described in this section.

For MX Series routers, the normalized VLAN is specified using one of the following configuration statements in the VPLS routing instance:

• vlan-id vlan-number
• vlan-id none
• vlan-tags outer outer-vlan-number inner inner-vlan-number

You must configure vlan-maps explicitly on all interfaces belonging to the routing instance.

The following forwarding path considerations must be observed:

• Packet receive path:
  • This is the forwarding path for packets received on the interfaces.
  • 802.1ag Ethernet OAM for VPLS uses implicit interface filters and forwarding table filters to flood, accept, and drop the CFM packets.
• Packet transmit path:
  • The JUNOS Software uses the router’s hardware-based forwarding for CPU-generated packets.
  • For Down MEPs, the packets are transmitted on the interface on which the MEP is configured.
  • For Up MEPs, the packet must be flooded to other interfaces in the VPLS routing instance. The router creates a flood route tied to a flood next hop (with all interfaces to flood) and then sources the packet to be forwarded with this flood route.
  • The router also uses implicit-based forwarding for CPU generated packets. The result is for the flood next hop tied to the flood route to be tied to the filter term. The filter term uses match criteria to correctly identify the host- generated packets.