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▀ Supported LAC Service Configurations for the GGSN and P-GW
1. A Create PDP Context Request message for a subscriber session is sent from the SGSN to the GGSN service
over the Gn interface. The message contains information such as the PDP Type, APN, and charging
characteristics.
2. The GGSN determines whether or not it is configured with an APN identical to the one specified in the message.
If so, it determines how to process the session based on the configuration of the APN.
The APN configuration indicates such things as the IP address of the LNS, the system destination context in
which a LAC service is configured.
Note that L2TP support could also be configured in the subscriber's profile. If the APN is not configured for
L2TP tunneling, the system will attempt to authenticate the subscriber.The tunneling parameters in the
subscriber's profile would then be used to determine the peer LNS.
3. The GGSN returns an affirmative Create PDP Context Response to the SGSN over the Gn interface.
4. The GGSN passes the PPP packets received from the MS to a LAC service.
5. The LAC service encapsulates the PPP packets and forwards it to the appropriate Gi interface for delivery to the
LNS.
6. The LNS un-encapsulates the packets and processes them as needed. The processing includes PPP termination,
authentication (using the username/password provided by the subscriber), and IP address allocation.
Configuring the GGSN or P-GW to Support L2TP
This section provides a list of the steps required to configure the GGSN or P-GW to support L2TP. Each step listed
refers to a different section containing the specific instructions for completing the required procedure.
Important:
sessions as a GGSN or P-GW.
1. Configure the APN template to support L2TP tunneling according to the information and instructions located in
the Modifying APN Templates to Support L2TP section of this chapter.
2. Configure one or more LAC services according to the information and instructions located in the Configuring
LAC Services section of this chapter.
3. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec
mode command
files, refer to the System Administration Guide and the Command Line Interface Reference.
▄ Cisco ASR 5x00 Packet Data Network Gateway Administration Guide
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These instructions assume that the system was previously configured to support subscriber data
Important:
L2TP tunneling can be configured within individual subscriber profiles as
opposed/or in addition to configuring support with an APN template. Subscriber profile
configuration is described in the Configuring Subscriber Profiles for L2TP Support section of this
chapter.
save configuration
. For additional information on how to verify and save configuration
L2TP Access Concentrator
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