A Metro Ethernet Network with MX Series Routers

The VLAN labels in the packet are stacked with MPLS labels, as shown in Figure 1. For a more detailed examination of this type of Metro Ethernet network, see Example: Configuring a Provider VPLS Network with Normalized VLAN Tags.

Figure 1: A Metro Ethernet Network

Another possible configuration, this one without the VPLS and MPLS core, is shown in Figure 2.

Figure 2: A Metro Ethernet Network with MX Series Routers

In Figure 2, the circled numbers reflect the different formats that the Ethernet frames can take as the frames make their way from a host on one Ethernet switching hub to a host on the other hub. The frame can have two VLAN tags (inner and outer), one tag (only the inner), or no tags at all. The structure of these various Ethernet frames is shown in Figure 3.

Figure 3: VLAN Tags on a Metro Ethernet Network

• No VLAN tags—At locations 1 and 5, the Ethernet frames can be native and have no VLAN tags at all (many NIC cards can include configuration of a VLAN identifier, but not all).
• One VLAN tag—At locations 2 and 4, from the VLAN-aware switching hub to the MX Series router, the Ethernet frame has one VLAN tag (if a VLAN tag is not present on arriving frames, a tag is added by the MX Series router).
• Two VLAN tags—At location 3, between two provider bridges, the MX Series routers exchange frames with two VLAN tags. The outer tags are added and removed by the MX Series routers.