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Chapter 6
Configuring the Line Interface
Configuring L2TP IP Tunnels
By default, IP tunnel recognition is disabled.
The IP tunneling mode is mutually exclusive with VPN-based classification.
How to Enable IP Tunnels
Use this command to configure recognition of L2TP tunnels and skipping into the internal IP packet.
From the SCE(config if)# prompt, type ip-tunnel L2TP skip and press Enter.
Step 1
How to Disable IP Tunnels
Step 1
From the SCE(config if)# prompt, type no ip-tunnel and press Enter.
IPinIP Tunneling
IPinIP is an IP-based tunneling protocol; therefore the system must be specifically configured to
recognize the flows inside the tunnel. The SCE platform will then skip the external IP header, reaching
the internal IP, which is the actual subscriber traffic. When IPinIP skip is disabled, the system treats the
external IP header as the subscriber traffic, resulting in all IPinIP traffic being reported as generic IP.
Guidelines for configuring IPinIP tunnels:
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Fragmentation
Fragmentation should be avoided whenever possible. If it is not possible to avoid fragmentation, it is
recommended to opt for internal fragmentation. If that is also not possible, the SCE platform can be
operated under conditions of external fragmentation.
OL-7827-12
IPinIP and other tunnels: IPinIP is supported simultaneously with plain IP traffic and any other
tunneling protocol supported by the SCE platform.
Overlapping IP addresses: There is no support for overlapping IP addresses within different IPinIP
tunnels.
DSCP marking: For IPinIP traffic, DSCP marking can be done on either the external or the internal
IP header exclusively.
Cisco SCE 2000 and SCE 1000 Software Configuration Guide
Tunneling Protocols
6-7
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