- Overview of Dial Interfaces, Controllers, and Lines
- Configuring Asynchronous Lines and Interfaces
- Asynchronous Call Queueing by Role
- Configuring Asynchronous Serial Traffic Over UDP
- Configuring and Managing Integrated Modems
- 1- and 2-Port V.90 Modem WICs for Cisco 2600 and Cisco 3600 Series Multiservice Platforms
- Call Tracker show Commands Extensions
- Cisco NM-8AM-V2 and NM-16AM-V2 Analog Modem Network Modules with V.92
- MICA and NextPort Modem Tech-Support Command Additions
- PIAFS Wireless Data Protocol Version 2.1 for Cisco MICA Modems
- V.92 and V.44 Support for Digital Modems
- V.92 Modem on Hold for Cisco AS5300 and Cisco AS5800 Universal Access Servers
- V.92 Modem on Hold for Cisco AS5350, Cisco AS5400, and Cisco AS5850 Universal Gateways and Cisco AS5800 Universal Access Servers
- V.92 Quick Connect for Cisco AS5300 and Cisco AS5800 Universal Access Servers
- V.92 Quick Connect for Cisco AS5350, Cisco AS5400, and Cisco AS5850 Universal Gateways and Cisco AS5800 Universal Access Servers
- V.92 Reporting Using RADIUS Attribute v.92-info
- Configuring and Managing Cisco Access Servers and Dial Shelves
- Configuring and Managing External Modems
- Modem Signal and Line States
- Creating and Using Modem Chat Scripts
- Cisco Modem User Interface
- Modem Script and System Script Support in Large-Scale Dial-Out
- Leased and Switched BRI Interface for ETSI NET3
- ISDN BCAC and Round-Robin Channel Selection Enhancements
- Configuring Virtual Asynchronous Traffic over ISDN
- Configuring Modem Use over ISDN BRI
- Configuring X.25 on ISDN
- Configuring X.25 on ISDN Using AO/DI
- Configuring ISDN on Cisco 800 Series Routers
- Cisco IOS Software Feature Removal
- Configuring ISDN PRI
- Dialing Number Enhancement
- ISDN BCAC and Round-Robin Channel Selection Enhancements
- Configuring ISDN Special Signaling
- Configuring Network Side ISDN PRI Signaling, Trunking, and Switching
- Preparing to Configure DDR
- Configuring Legacy DDR Spokes
- Configuring Legacy DDR Hubs
- Configuring Peer-to-Peer DDR with Dialer Profiles
- Dialer Map VRF-Aware for an MPLS VPN
- Dialer Persistent
- PPPoE Client DDR Idle-Timer
- Redial Enhancements
- Rotating Through Dial Strings
- Configuring Dialer CEF
- CEF Support for Dialer Profiles on Cisco 7500 Routers
- Configuring Snapshot Routing
- Reliable Static Routing Backup Using Object Tracking
- Configuring Dial Backup for Serial Lines
- Configuring Dial Backup Using Dialer Watch
- Dialer Watch Connect Delay
- VRF Aware Dialer Watch
- Configuring Dial Backup with Dialer Profiles
- ISDN Backup in MPLS Core
- Configuring Cisco Easy IP ..
- Configuring Virtual Template Interfaces
- Multiclass Multilink PPP
- Configuring Asynchronous Callback
- Configuring PPP Callback
- Configuring ISDN Caller ID Callback
- Configuring BACP
- Configuring an IP Local Pools Holdback Timer
- Configuring per-User Configuration
- Configuring Resource Pool Management
- Configuring Wholesale Dial Performance Optimization
- Large-Scale Dial-Out
- Dial-Out DS0 Level Trunk Group
- L2TP Large-Scale Dial-Out
- L2TP Large-Scale Dial-Out per-User Attribute via AAA
- Modem Script and System Script Support in Large-Scale Dial-Out
- Large-Scale Dial-Out (LSDO) VRF Aware
- Peer Pool Backup
- Dial Networking Business Applications
- Enterprise Dial Scenarios and Configurations
- Telco and ISP Typical Dial Scenarios and Configurations
- Modem Initialization Strings
L2TP Large-Scale Dial-Out
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This feature was implemented on Cisco access server platforms. |
This document describes the L2TP Large-Scale Dial-Out feature. It includes the following sections:
Feature Overview
The Asynchronous Line Monitoring feature feature enables the router to dial multiple Layer 2 Tunnel Protocol (L2TP) access concentrators (LACs) from a single L2TP network server (LNS). The LACs are signaled through the LNS and use L2TP to establish the dial sessions. User-defined profiles can be configured on an authentication, authorization, and accounting (AAA) server and retrieved by the LNS when dial-out occurs.The Asynchronous Line Monitoring feature feature also supports multiple LACs bound into one stack group, call traffic load balancing, and outbound call congestion management.
Figure 1 provides an example of L2TP large-scale dial-out session startup. Each part of the process is numbered and described in text following the figure.
Figure 1 Sample Scenario L2TP Large-Scale Dial-Out Session
1.
The IP packets arrive at the LNS and are forwarded to the dialer interface by the routing protocol. (A virtual access interface has not been created yet.)
2. A dialer session is created and placed in a pending state while the dialer interface sends a Dial Out Request message to the AAA server requesting the user profile. The AAA server sends the user profile, and the LNS builds a dynamic map based on the reply.
3. The dialer interface looks for its dial resources and finds the virtual private dialup network (VPDN) group. The dialer interface then issues a dial call request to the VPDN group, which creates a virtual access interface. The virtual access interface becomes a member of a rotary group.
4. If there is no existing L2TP tunnel between the LNS and the primary LAC, the LNS would establish one; otherwise, it uses the existing tunnel. The LNS sends an Outgoing Call ReQuest (OCRQ) message, inside of which is the dynamic dialer map, to the primary LAC.
5. Upon receiving the OCRQ message, the primary LAC determines whether it is congested. If the primary LAC is congested, it sends a Stack Group Bidding Protocol (SGBP) Discover message through a new tunnel to the secondary LAC in the scenario depicted in Figure 1, but it could send the message to any other LAC configured in the SGBP stack group.
After the secondary LAC receives the SGBP Discover message from the LNS, it responds with an SGBP Offer message describing available resources.
6. If neither LAC has resources to dial out, the primary LAC would send a Call Disconnect Notification (CDN) message to the LNS. The LNS would then tear down the tunnel.
If the secondary LAC has more resources, the primary LAC can choose to dial through the secondary LAC. The primary LAC sends a CDN message to the LNS with error code 7, which means “Try another” as defined in RFC 2661. Inside this message, the LNS learns that its dial-out request should be redirected to the secondary LAC, and the LNS clears the session to the primary LAC.
7. The LNS creates a new tunnel to the secondary LAC if one does not exist. The dial-out LAC creates a VPDN session and sets it in a pending state. It then places a call to the PPP client. Once the call is connected, the LAC determines to which pending VPDN session the connected interface belongs and binds the connected interface with the session. The secondary LAC sends an Outgoing Call Connected (OCCN) message to the LNS. The LNS determines for which pending virtual access interface and VPDN session this OCCN is meant, and then the LNS brings up the virtual access interface.
Benefits
Large-Scale Dial-Out Integrated with L2TP
Before Cisco IOS Release 12.2(4)T, L2TP required that requests for tunneled dial-out calls be from a single LNS to a single LAC, and that configurations be available on the local server. The Asynchronous Line Monitoring feature feature introduced in Cisco IOS Release 12.2(4)T allows dialing multiple LACs from a single LNS. The LACs are signaled through the LNS using L2TP to establish the dial sessions. User-defined profiles can also be configured on a AAA server and retrieved by the LNS when dial-out occurs.
The Asynchronous Line Monitoring feature feature also provides the following benefits:
Related Features and Technologies
L2TP, VPDNs, and large-scale dial-out are described in the Cisco IOS Dial Technologies Configuration Guide, Release 12.2. Refer to the chapter “Configuring Virtual Private Networks” in the part “Virtual Templates, Profiles, and Networks,” and the chapter “Configuring Large-Scale Dial-Out” in the part “Dial Access Specialized Features.”
Supported Platforms
See the next section for information about Feature Navigator and how to use this tool to determine the platforms and software images in which this feature is available.
Platform Support Through Feature Navigator
Cisco IOS software is packaged in feature sets that support specific platforms. To get updated information regarding platform support for this feature, access Feature Navigator. Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.
Feature Navigator is a web-based tool that enables you to quickly determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image.
To access Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions at http://www.cisco.com/register.
Feature Navigator is updated when major Cisco IOS software releases and technology releases occur. As of May 2001, Feature Navigator supports M, T, E, S, and ST releases. You can access Feature Navigator at the following URL:
Supported Standards, MIBs, and RFCs
To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
Configuration Tasks
See the following sections for configuration tasks for the Asynchronous Line Monitoring feature feature. Each task in the list is identified as either required or optional:
- Configuring the LNS to Request Dial-Out (required)
- Configuring a LAC to Accept Dial-Out (required)
Configuring the LNS to Request Dial-Out
Virtual profiles depend on PPP authentication; therefore the LNS must authenticate the connection to use virtual profiles.
You must configure AAA network security services on the LNS. For more information about AAA, refer to the chapter “AAA Overview” in the Cisco IOS Security Configuration Guide, Release 12.2. The Cisco IOS Security Command Reference, Release 12.2, describes the commands to configure AAA.
You also need to configure your LNS to communicate with the applicable security server, either a TACACS+ or RADIUS daemon.
If you are using RADIUS and Ascend attributes, use the radius-server host non-standard global configuration command to enable your Cisco router, acting as a network access server, to recognize that the RADIUS security server is using a vendor-proprietary version of RADIUS. Use the radius-server key global configuration command to specify the shared secret text string used between your Cisco router and the RADIUS server. For more information, refer to the chapter “Configuring RADIUS” in the Cisco IOS Security Configuration Guide, Release 12.2.
If you are using TACACS+, use the tacacs-server host global configuration command to specify the IP address of one or more TACACS+ daemons. Use the tacacs-server key global configuration command to specify the shared secret text string used between your Cisco router and the TACACS+ daemon. For more information, see the Cisco IOS Security Configuration Guide, Release 12.2.
To configure the LNS to request dial-out tunneled PPP connections from a LAC, use the following commands beginning in global configuration mode:
The MLP feature provides load-balancing functionality over multiple WAN links and offers load calculation on both inbound and outbound traffic. Refer to the part “PPP Configuration” and the chapter “Configuring Media-Independent PPP and Multilink PPP” in the Cisco IOS Dial Technologies Configuration Guide, Release 12.2, for more information.
See the configuration examples later in this document for additional commands that may be configured on the LAC.
Configuring a LAC to Accept Dial-Out
You must configure SGBP to allow a primary LAC that is congested or otherwise unable to dial out to select an alternate LAC to dial out. Configure SGBP using the sgbp group and sgbp member global configuration commands before enabling the stack group to bid for dial-out connection. Configuring SGBP is described in the chapter “Configuring Multichassis Multilink PPP” in the Cisco IOS Dial Technologies Configuration Guide, Release 12.2. The Cisco IOS Dial Technologies Command Reference, Release 12.2, describes the commands to configure a stack group.
Additionally, the information about configuring network security in the section “Configuring the LNS to Request Dial-Out” of this document also applies to configuring the LAC.
To configure a LAC to accept tunneled dial-out connections from the LNS, use the following commands beginning in global configuration mode:
See the configuration examples later in this document for additional commands that may be configured on the LAC.
Verifying L2TP Large-Scale Dial-Out
To verify that L2TP large-scale dial-out is configured correctly, perform the following steps:
Note Effective with Cisco Release 12.4(11)T, the L2F protocol was removed in Cisco IOS software.
Step 1 From the LNS, display tunnel statistics by entering the show vpdn and the show vpdn tunnel all EXEC commands:
Step 2 From the LNS, enter the show interfaces virtual-access EXEC command to verify that the interface is up and that no errors are reported:
Step 3 From the LNS, display information for MLP bundles by entering the show ppp multilink EXEC command:
Step 4 From the LAC, display active tunnel statistics by entering the show vpdn and show vpdn tunnel all EXEC commands:
Step 5 From the LAC, confirm active SGBP group members by entering the show sgbp EXEC command:
Step 6 From the LAC, display connection status by entering the show isdn status EXEC command or the show user EXEC command:
Monitoring and Maintaining L2TP Large-Scale Dial-Out
To monitor and maintain L2TP large-scale dial-out, use the following EXEC commands:
Configuration Examples
This section provides the following configuration examples:
LNS Configured to Request Dial-Out Example
In the following example, the LNS VPDN group is configured to make a dial-out request using L2TP:
LAC Configured to Accept Dial-Out Example
In the following example, the VPDN group of a LAC is configured to accept dial-outs using L2TP as the tunneling protocol and dialer interface 2:
Command Reference
This feature uses no new or modified commands. For information about all Cisco IOS commands, go to the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or to the Cisco IOS Master Commands List.
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