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Tunneling Protocols
Table 6-1
is in bold).
Table 6-1
Protocol Supported handling
L2TP
IPinIP
VLAN
MPLS
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.
For directions on how to configure the asymmetric tunneling option, see
Note
page 6-13
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.
Cisco SCE 2000 and SCE 1000 Software Configuration Guide
6-4
shows the support for the various tunneling protocols (the default behavior for each protocol
Tunneling Protocol Summary
Ignore tunnel
Don't ignore tunnel – classify by
external IP
Ignore tunnel
Don't ignore tunnel – classify by
external IP
Ignore tunnel
Ignore tunnel – asymmetric
VLAN tag used for VPN
classification
Ignore tunnel (inject unlabeled)
Ignore tunnel (inject labeled)
MPLS labels used for VPN
classification
Chapter 6
Mode name
IP-tunnel L2TP skip
No IP-tunnel
ip-tunnel IPinIP skip
no ip-tunnel IPinIP skip
VLAN symmetric skip
VLAN asymmetric skip
VLAN symmetric classify
MPLS traffic-engineering skip
MPLS VPN skip
MPLS VPN auto-learn
Table
Configuring the Line Interface
Symmetric/
Asymmetric
asymmetric
symmetric
symmetric
symmetric
symmetric
asymmetric
symmetric
symmetric
asymmetric
symmetric
6-1). Any time that one of
Asymmetric L2 Support,
OL-7827-12
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