Cisco SCE 8000 10GBE Software Configuration Manual page 197

Chapter 7 Configuring Line Interfaces
Tunneling Protocols
When the tunneling information is ignored, the subscriber identification is the subscriber IP of the IP
packet carried inside the tunnel.
Asymmetric Tunneling
Some tunneling modes are symmetric and some are asymmetric (see Table 7-1). Any time that one of
the asymmetric tunneling modes is enabled, the entire system is automatically set to asymmetric flow
open mode. In this mode, flows are opened earlier than in symmetric flow open mode, and the first packet
of each direction of the flow (upstream and downstream) reaches the software. This has some impact on
both performance and capacity, so that a certain performance degradation should be expected in any
asymmetric mode.
You can explicitly configure the system to treat all flows as having asymmetric layer 2 characteristics
(including Ethernet, VLAN, MPLS, and L2TP).
To view the effective flow open mode, use the show interface linecard 0 flow-open-mode command.
For directions on how to configure the asymmetric tunneling option, see "Asymmetric L2 Support"
Note
section on page 7-18
L2TP
L2TP is an IP-based tunneling protocol, therefore the system must be specifically configured to
recognize the L2TP flows, given the UDP port used for L2TP. The Cisco SCE platform can then skip the
external IP, UDP, and L2TP headers, reaching the internal IP, which is the actual subscriber traffic. If
L2TP is not configured, the system treats the external IP header as the subscriber traffic, thus all the
flows in the tunnel are seen as a single flow.
VLAN
A single VLAN tag is supported per packet (no QinQ support).
Subscriber classification by VLAN tag is supported only in symmetric VLAN environments, that is, in
environments where the upstream and downstream tags of a flow are identical.
Cisco SCE 8000 10GBE Software Configuration Guide
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