Selecting The Tunneling Mode; How To Configure Ip Tunnels - Cisco SCE8000 Configuration Manual

Chapter 6 Configuring the Line Interface
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
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 is required
to support redirect and block operations over asymmetric layer 2 protocols. However, it also has some
performance impact, so that a certain performance degradation should be expected in any asymmetric
mode.
It is also possible to explicitly configure the system to treat all flows as having asymmetric layer 2
characteristics (including Ethernet, VLAN, MPLS, and L2TP), for the purpose of packet injection (such
as block flow and redirect flow operations).
To view the effective flow open mode, use the show interface linecard 0 flow-open-mode command.
Note For directions on how to configure the asymmetric tunneling option, see
page 6-7
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 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 – i.e. where
the upstream and downstream tags of a flow are identical.

Selecting the Tunneling Mode

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Use these commands to configure tunneling:
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OL-16479-02
How to Configure IP Tunnels, page 6-4
IPinIP Tunneling, page 6-4
How to Configure the VLAN Environment, page 6-6
How to Configure the L2TP Environment, page 6-6
ip-tunnel
vlan
L2TP identify-by
Table 6-1). Any time that one of
Asymmetric L2 Support,
Cisco SCE8000 Software Configuration Guide
Tunneling Protocols
6-3