MX Series Router ATM Ethernet Interworking Function
You can configure an MX Series router as part of an ATM Ethernet interworking function (IWF) scenario mapping outer and inner VLAN tags to ATM Virtual Path Identifier (VPI) and Virtual Channel Identifier (/VCI).
The ATM Ethernet interworking scenario is shown in Figure 1. The MX Series router is configured as the Provider Edge 2 (PE2) router in the figure to support the ATM Ethernet IWF. Ethernet is the only transport type supported.
Figure 1: ATM Ethernet VLAN Interworking
The PE1 router translates between ATM and Ethernet VLANs. Only an M Series router can function as the PE1 router.
The PE1 router translates between the ATM VPI and VCI and Ethernet VLAN tags as follows:
- ATM VPI to and from outer VLAN tag of the Ethernet frame
- ATM VCI to and from inner VLAN tag of the Ethernet frame
Because of the translation, the flow of packets and frames between PE1 (the M Series router) and PE2 (the MX series router) routers is not symmetrical, as is shown in Figure 2.
Figure 2: ATM Ethernet VLAN Interworking Packet Structure
For PE1 to PE2 traffic, the 8 bytes following the MPLS header is an ATM cookie added by the M Series ATM PIC. The first two bytes are the inner VLAN tag, which is why the field extends to the right of the figure.
The traffic between PE2 and CE2 is a normal flow of stacked Ethernet frames.
You can also configure a CCC with remote interface switch or Layer 2 circuit over Aggregated Ethernet on the MX Series router (PE2). When CCC is configured for Aggregated Ethernet, the flow of packets is as shown in Figure 3.
Figure 3: CCC-to-Stacked VLAN Translation
