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However, this mode of processing did not allow for:
Identification of a particular VLAN tag in single-tagged or double-tagged packets as
the service-delimiting tag
Selective removal of only the service-delimiting tag when layer 2 frames were received
from the CE devices to be sent to the pseudowire
Selective insertion of only the service-delimiting tag when layer 2 frames were received
from the pseudowire to be sent to the CE device
In this release, you can configure an S-VLAN subinterface to enable the provider edge
(PE) device to strip the S-VLAN tag from all packets that enter the MPLS pseudowires
or Martini circuits. This functionality is also referred to as operation of Martini circuits or
MPLS shim interfaces in raw mode. An Ethernet pseudowire can operate in either tagged
mode or raw mode.
In tagged mode, each frame must contain at least one 802.1Q VLAN tag, and the tag
value is processed based on a predefined rule or algorithm at the two pseudowire end
points. This mode is not supported on E Series routers.
In raw mode, if a frame contains an 802.1Q VLAN tag and the tag is not suitable to be
processed at the two pseudowire end points, it passes transparently through them.
The raw mode operation comprises the following tasks:
Identifying the outermost VLAN tag of the layer 2 frame received from the attachment
circuit as a service-delimiting tag, stripping this tag, and then inserting the resulting
frame into the pseudowire connection
Inserting the specified service-delimiting tag on the layer 2 frame received from the
pseudowire connection and then transmitting the resulting frame to the attachment
circuit
You can enable the raw mode configuration only for MPLS shim interfaces stacked on
S-VLAN interfaces. Unified ISSU and high availablity are supported when the router is
configured in either of these ways:
To strip the S-VLAN tags from all packets that enter Martini circuits
When raw mode encapsulation is configured on the VLAN interface stacked below the
MPLS shim interface
When a pseudowire operates in raw mode, service-delimiting tags, if present in the frame
received from the PE device, are stripped from the frame before being sent to the next
processing point in the circuit. The Ethernet frame is encapsulated according to the
algorithm defined for raw mode. If the local PE device detects a failure on the Ethernet
input port, or if the port is disabled, the PE device sends an appropriate pseudowire status
notification message to the remote PE device. In raw mode, all Ethernet frames received
on the local PE device are transmitted to the remote PE device on a single pseudowire.
The raw-mode attribute of the Martini circuit is sent to the forwarding controller (FC) on
the supported line modules and the Label Distribution Protocol (LDP) is notified of the
correct pseudowire type to be used in the signaling messages.
Chapter 8: Layer 2 Services over MPLS Overview
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