Figure 3: A Metro Ethernet Network With Mx Series Routers; Figure 4: Vlan Tags On A Metro Ethernet Network - Juniper JUNOS OS 10.4 Manual

Junos OS 12.1 MX Series 3D Universal Edge Routers Solutions Guide
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16

Figure 3: A Metro Ethernet Network with MX Series Routers

In Figure 3 on page 16, 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 on page

Figure 4: VLAN Tags on a Metro Ethernet Network

As the frame flows from a LAN-based host on one end of
the Ethernet frame can have:
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.
Ethernet Networking
Ethernet Terms and Acronyms on page 3
Networking and Internetworking with Bridges and Routers on page 6
Network Addressing at Layer 2 and Layer 3 on page 7
16.
Figure 4 on page 16 to the other,
Copyright © 2012, Juniper Networks, Inc.