What would a Metro Ethernet network with MX-series routers look like? It is very likely that the Metro Ethernet network will place MX-series routers at the edge of a VPLS and MPLS core network. The VLAN labels in the packet are stacked with MPLS labels, as shown in Figure 2. For a more detailed examination of this type of Metro Ethernet network, see VPLS Labels and VLAN Tags.
Figure 2: A Metro Ethernet Network
Another possible configuration, this one without the VPLS and MPLS core, is shown in Figure 3.
Figure 3: A Metro Ethernet Network with MX-series Routers
In Figure 3, 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 4.
Figure 4: VLAN Tags on a Metro Ethernet Network
As the frame flows from a LAN-based host on one end of Figure 4 to the other, the Ethernet frame can have:
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