Examples: Ethernet Raw Mode Encapsulation for Martini Layer 2 Transport

When a Martini circuit operates in Ethernet raw mode, you can configure the provider edge (PE) devices that receive packets from the customer edge (CE)-facing devices to remove the S-VLAN tags from all packets entering the circuit. A device or network is said to be S-VLAN-aware, if the packets passed through it contain the S-VLAN tag configured on the subinterface. Similarly, if the S-VLAN tag is not configured on the subinterface, the device is said to be S-VLAN-unaware of the packet reaching it because the S-VLAN tag is not passed to it.

A particular S-VLAN tag that is identified as the service-delimiting tag is removed from the incoming Ethernet frame from the CE device before it is sent on the pseudowires. In this release, only raw mode operation is supported on the S-VLAN subinterfaces of PE routers. Therefore, scenarios in which the S-VLAN tag is made available to the MPLS network and the S-VLAN tag is not advertised to the CE device are not supported. Depending on how Ethernet raw mode is configured on PE devices and the configuration of the S-VLAN subinterface on CE-facing devices, a device in the Maritni circuit can be either S-VLAN-aware or S-VLAN-unaware.

Figure 1 shows a Martini circuit deployment in which the CE-side devices on either side of the network send and receive Ethernet frames. The packets reaching the CE-side devices can be S-VLAN-aware or not. The MPLS network might also be S-VLAN-aware or not, which means that S-VLAN tags might or might not be sent over the MPLS cloud.

Figure 1: MPLS L2VPN Tunnel over LAG Configuration Example

The cases in which the MPLS network is S-VLAN-aware, but the CE-side device is not S-VLAN-aware, are supported because the Ethernet pseudowire operates in tagged mode. When the pseudowire is configured for raw mode, only two cases are supported: whether the CE-side device is S-VLAN-aware or not aware.

Table 1 describes the different scenarios in which the Martini circuit shown in Figure 1 can be deployed depending on whether the various network segments are S-VLAN-aware or not.

Table 2 describes the different scenarios in which the Martini circuit configuration is supported, when Ethernet raw mode encapsulation is configured on the S-VLAN interfaces.

Figure 2 shows the transmission of Ethernet packets over a Martini circuit with ES2 4G, GE-2, GE/FE, ES2 10G, ES2 10G Uplink, and ES2 10G ADV LMs. The different processing points inside the PE-facing routers are denoted as A, B, C, and D.

Figure 2: Ethernet Packet Distribution over Martini Circuits

Consider a scenario in which Ethernet raw mode is not enabled on the S-VLAN subinterface of the PE-facing devices. When a packet reaches the S-VLAN subinterface on an ingress line module, point A, inside PE1, all packets, regardless of whether they are tagged or not, are forwarded to the subinterface on the egress line module, B, inside PE1 without any change. This behavior applies to both ES2 4G LMs, ES2 10G LMs, ES2 10G Uplink LMs, and ES2 10G ADV LMs. At point B, the MPLS encapsulation header is added to the packet and the egress line module forwards it to the MPLS network. This functionality is the same for both ES2 4G, ES2 10G, ES2 10G Uplink, and ES2 10G ADV LMs. When the packet reaches the subinterface on the ingress line module (ES2 4G LM and ES2 10G LM), point C, inside PE2, the added MPLS header is removed and the packet is sent to the subinterface on the egress line module, point D, for further processing. At point D, for ES2 4G LMs, the packet is sent to the remote CE-facing device, depending on the configuration of the S-VLAN subinterface. If the packet arrives with a single or no tag, the router adds the S-VLAN tag and sends it to the CE-facing device. On ES2 10G LMs, ES2 10G Uplink LMs, and ES2 10G ADV LMs, at point D, the packet is forwarded to the CE-facing device without any modification.

In the same scenario, when Ethernet raw mode is enabled on the S-VLAN subinterface of the PE devices, the processing of Ethernet packets is performed in a slightly different way. At the S-VLAN subinterface on an ingress ES2 4G LM, ES2 10G LM, ES2 10G Uplink LM, and ES2 10G ADV LM, point A, inside PE1, the S-VLAN tag is removed from the received packet before being forwarded to the subinterface on the egress line module, B, inside PE1. At point B, the MPLS encapsulation header is added to the packet and the egress line module forwards it to the MPLS network. This functionality is the same for both ES2 4G LMs ,ES2 10G LMs, ES2 10G Uplink LMs, and ES2 10G ADV LMs. When the packet reaches the subinterface on the ingress ES2 4G LMs, ES2 10G LMs, ES2 10G Uplink LMs, and ES2 10G ADV LMs, point C, inside PE2, the added MPLS header is removed and the packet is sent to the subinterface on the egress line module, point D, for further processing. This behavior is the same, regardless of whether raw mode encapsulation is enabled or not. At point D, for both ES2 4G LMs, ES2 10G LMs, ES2 10G Uplink LMs, and ES2 10G ADV LMs, the S-VLAN tag is inserted into the packet and sent to the CE-facing device at the remote site.