The ASR 1000
platform services as the SP broadband network gateway which:
Figure 1. Ethernet over Soft GRE Deployment
The deployment model that is supported is the two-box model:
The major components involved in L2 EoGRE are:
Virtual Ethernet interface.
Ethernet service instance.
IP GRE tunnel data plane.
L2 bridge-domain data plane.
Control Plane—After the Virtual Ethernet interface is configured,
the Virtual Ethernet interface is downloaded to the ASR 1000 platform as a
Service instances (EVCs) are configured under the virtual ethernet
interface and are downloaded to ASR1K platform. The service instances are then
propagated in the ASR 1000 platform to fman-rp, fman-fp, cpp-client and cpp
dataplane, where the EVC feature invocation arrays (FIAs) are enabled.
Data Plane—When receiving the IP GRE encapsulated Ethernet
packet, the data plane tunnel ingress processing checks the protocol field in
the GRE header. If the protocol is transparent Ethernet bridging protocol
(0x6558), the packet is identified as Ethernet over soft GRE packet and is
directed to the Ethernet service instance classification module. The Ethernet
service instance classification module classifies the packet into the service
instance configured under the Virtual Ethernet interface using the VLAN tag in
the packet. After the Ethernet service instance is identified, the packet goes
through the programmed processing FIA under the Ethernet service instance such
as vlan tag manipulation and is then sent to L2 bridge domain for further
processing. At the L2 bridge domain processing module, the client source MAC
address is dynamically learned, and so is the IP GRE tunnel end-points. As a
result, the MAC address table contains the IP GRE tunnel end-points for the
client MAC address.
The packet is then either bridged to the external ISG for subscriber
processing in the case of the two-box deployment model. In the direction where
the ISG, either external or internal, sends a packet to the mobile client, the
L2 bridge domain looks up the destination MAC address using the L2 bridge
domain MAC address table. Once the result is found, the IP GRE tunnel end point
addresses are also retrieved from the MAC address table. The L2 Ethernet packet
is then encapsulated into the IP GRE tunnel using the retrieved tunnel end
point address. Once encapsulated into the IP GRE packet, IP lookup is then
performed and the packet is sent to the CPE.