Table Of Contents
L2TP Dial-Out Load Balancing and Redundancy
Restrictions for L2TP Dial-Out Load Balancing and Redundancy
Information About L2TP Dial-Out Load Balancing and Redundancy
Dial-Out and Multiple LACs on the LNS
L2TP Load Balancing and Redundancy
How to Configure L2TP Dial-Out Load Balancing and Redundancy
Configuring Multiple LACs on the LNS
Configuration Examples for L2TP Dial-Out Load Balancing and Redundancy
L2TP Dial-Out Load Balancing Example
L2TP Dial-Out Failover Redundancy Example
L2TP Dial-Out Failover Redundancy with Tunnel Timers Example
L2TP Dial-Out Load Balancing and Redundancy
The L2TP Dial-Out Load Balancing and Redundancy feature enables an L2TP network server (LNS) to dial out to multiple L2TP access concentrators (LACs). When the LAC with the highest priority goes down, it is possible for the LNS to failover to another lower priority LAC. The LNS can also load balance the sessions between multiple LACs that have the same priority settings.
Feature Specifications for L2TP Dial-Out Load Balancing and Redundancy
12.2(15)T
This feature was introduced.
Cisco 7200, Cisco 7400
Finding Support Information for Platforms and Cisco IOS Software Images
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Contents
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Restrictions for L2TP Dial-Out Load Balancing and Redundancy
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Restrictions for L2TP Dial-Out Load Balancing and Redundancy
Because multiple LACs are configured using the same virtual private dial-up network (VPDN) group, they must have the same tunnel configuration settings (the same L2TP tunnel password, for example).
Information About L2TP Dial-Out Load Balancing and Redundancy
To configure the L2TP Dial-Out Load Balancing and Redundancy feature, you need to understand the following concepts:
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Dial-Out and Multiple LACs on the LNS
In Cisco IOS software prior to Release 12.2(15)T, Layer 2 Tunneling Protocol (L2TP) large-scale dial-out using the Stacked Group Bidding Protocol (SGBP) provided a different form of load balancing and redundancy. The LNS was configured with the IP address of the primary LAC using the initiate-to VPDN group configuration command. The LNS would initially contact the primary LAC, so therefore the primary LAC had to be up and running for dial-out to take place. When the primary LAC was down, no dial-out could take place. When the primary LAC was up, the LAC would determine among itself and the secondary LACs which LAC had the least congestion, and then inform the LNS to use the selected LAC for dial-out.
Additionally, the initiate-to VPDN group configuration command used to specify the IP address for the tunnel did not support multiple statements on an LNS; only the IP address of the primary LAC could be configured. Therefore, the LNS could not contact any other LACs when the primary LAC went down, and failover was not supported for dial-out calls by the LNS.
The L2TP Dial-Out Load Balancing and Redundancy feature introduced in Cisco IOS Release 12.2(15)T enables an LNS to dial out to multiple LACs (multiple initiate-to VPDN group configuration commands, and therefore multiple IP addresses, are supported).
L2TP Load Balancing and Redundancy
The L2TP Dial-Out Load Balancing and Redundancy feature supports load balancing between multiple LACs that have the same priority settings in the initiate-to VPDN group configuration commands. You can also set redundancy and failover by configuring differing priority values in the initiate-to VPDN group configuration commands. When the LAC with the highest priority goes down, the LNS will failover to another lower priority LAC.
How to Configure L2TP Dial-Out Load Balancing and Redundancy
This section contains the following required procedure:
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Configuring Multiple LACs on the LNS
To configure the L2TP Dial-Out Load Balancing and Redundancy feature, you configure multiple initiate-to command statements under a VPDN request dialout configuration. You will need to select the tunneling protocol and assign the VPDN subgroup to either a dial pool or rotary group. In most cases, defaults provided by the Cisco IOS software will configure the L2TP tunnel with the appropriate timers; however, you can use l2tp tunnel VPDN group configuration commands to change the default tunnel timer settings, if necessary.
Prerequisites
The L2TP Dial-Out Load Balancing and Redundancy feature provides additional functionality for large-scale dial-out networks and Layer 2 tunneling. It is assumed that a network is already configured and operational, and that the task in this document will be performed on an operating network. See the "Additional References" section for information about large-scale dial-out networks and Layer 2 tunneling.
To configure an LNS with multiple LACs for the L2TP Dial-Out Load Balancing and Redundancy feature, use the following commands. (Note that the l2tp tunnel commands are optional and should only be used if it becomes necessary to change the default settings for these commands.)
SUMMARY STEPS
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or
rotary-group group-number
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12.
DETAILED STEPS
Step 1
enable
Example:Router> enable
Enables privileged EXEC mode.
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Step 2
configure terminal
Example:Router# configure terminal
Enters global configuration mode.
Step 3
vpdn-group name
Example:Router(config)# vpdn-group 1
Creates a VPDN group and starts VPDN group configuration mode.
Step 4
request-dialout
Example:Router(config-vpdn)# request-dialout
Enables an LNS to request VPDN dial-out calls by using L2TP, and starts VPDN request-dialout configuration mode.
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Step 5
protocol l2tp
Example:Router(config-vpdn-req-ou)# protocol l2tp
Specifies the tunneling protocol that the VPDN subgroup will use. Configure L2TP for the the L2TP Dial-Out Load Balancing and Redundancy feature.
Step 6
pool-member pool-number
Example:Router(config-vpdn-req-ou)# pool-member 1
or
rotary-group group-number
Example:Router(config-vpdn-req-ou)# rotary-group 1
Assigns a request-dialout VPDN subgroup to a dialer pool.
or
Assigns a request-dialout VPDN subgroup to a dialer rotary group.
Step 7
exit
Example:Router(config-vpdn-req-ou)# exit
Exits VPDN request-dialout configuration mode.
Step 8
initiate-to ip ip-address [limit limit-number] [priority priority-number]
Example:Router(config-vpdn)# initiate-to ip 10.0.58.201 priority 1
Specifies the IP address that will be used for Layer 2 tunneling, and includes the following options:
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–
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Step 9
l2tp tunnel retransmit initial retries number
Example:Router(config-vpdn)# l2tp tunnel retransmit initial retries 5
(Optional) Sets the number of times that the router will attempt to send out the initial control packet for tunnel establishment before considering a router busy, in a range from 1 to 1000.
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Step 10
l2tp tunnel retransmit initial timeout {min | max} seconds
Example:Router(config-vpdn)# l2tp tunnel retransmit initial timeout min 4
(Optional) Sets the minimum or maximum amount of time that the router will wait before resending an initial packet out to establish a tunnel, in a range of from 1 to 8 seconds.
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Step 11
l2tp tunnel busy timeout seconds
Example:Router(config-vpdn)# l2tp tunnel busy timeout 420
(Optional) Configures the amount of time that the router will wait before attempting to recontact a router that was previously busy, in a range from 60 to 6000 seconds.
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Step 12
exit
Example:Router(config-vpdn)# exit
Exits VPDN group configuration mode.
Troubleshooting Tips
Use the show running-config EXEC command to display the configuration and check that the VPDN group and subgroups are configured correctly.
Configuration Examples for L2TP Dial-Out Load Balancing and Redundancy
This section provides the following configuration examples to show how the L2TP Dial-Out Load Balancing and Redundancy feature might be configured:
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L2TP Dial-Out Load Balancing Example
The following partial example shows how to configure multiple LACs on a LNS, and load balance calls to the LACs by assigning the same priority value to each in the initiate-to commands:
!vpdn enablevpdn search-order domain!vpdn-group 1...request-dialoutprotocol l2tppool-member 1initiate-to ip 10.0.58.201 priority 10initiate-to ip 10.0.58.205 priority 10initiate-to ip 10.0.58.207 priority 10initiate-to ip 10.0.58.209 priority 10...L2TP Dial-Out Failover Redundancy Example
The following partial example shows how to set priorities in the initiate-to command to configure redundant LACs that will be accessed by the LNS in the event of call failure. When the LAC with the highest priority goes down, the LNS will failover to another, lower priority LAC. The highest priority value you can assign to a LAC is 1.
!vpdn enablevpdn search-order domain!vpdn-group 1...request-dialoutprotocol l2tppool-member 1initiate-to ip 10.0.58.201 priority 1initiate-to ip 10.0.58.205 priority 100...L2TP Dial-Out Failover Redundancy with Tunnel Timers Example
The following partial example shows how to set parameters to control how many times an LNS will retry connecting to a LAC, and the amount of time after which the LAC will declare itself down or busy so that the LNS will try connecting to the next LAC:
!vpdn enablevpdn search-order domain!vpdn-group 1...request-dialoutprotocol l2tppool-member 1initiate-to ip 10.0.58.201 priority 1initiate-to ip 10.0.58.207 priority 50initiate-to ip 10.0.58.205 priority 100l2tp tunnel retransmit initial retries 5l2tp tunnel retransmit initial timeout min 4l2tp tunnel busy timeout 420...Additional References
For additional information related to L2TP Dial-Out Load Balancing and Redundancy, see the following sections:
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Related Documents
Large-scale dial-out
Cisco IOS Dial Technologies Configuration Guide, Release 12.2; refer to the chapter "Configuring Large-Scale Dial-Out."
Stack Group Bidding Protocol
Cisco IOS Dial Technologies Configuration Guide, Release 12.2; refer to the chapter "Configuring Multichassis Multilink PPP."
VPDN groups
Cisco IOS Dial Technologies Configuration Guide, Release 12.2; refer to the chapter "Configuring Virtual Private Networks."
Standards
MIBs
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
http://tools.cisco.com/ITDIT/MIBS/servlet/index
If Cisco MIB Locator does not support the MIB information that you need, you can also obtain a list of supported MIBs and download MIBs from the Cisco MIBs page at the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
To access Cisco MIB Locator, 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 found at this URL:
RFCs
Technical Assistance
Command Reference
This section documents the modified initiate-to VPDN group configuration command. All other commands used with this feature are documented in the Cisco IOS Release 12.2 T command reference publications.
initiate-to
To specify an IP address that will be used for Layer 2 tunneling, use the initiate-to command in VPDN group configuration mode. To remove an IP address from the VPDN group, use the no form of this command.
initiate-to ip ip-address [limit limit-number] [priority priority-number]
no initiate-to [ip ip-address]
Syntax Description
Defaults
This command is disabled.
Command Modes
VPDN group configuration
Command History
Usage Guidelines
Before you can use this command, you must enable one of the two request VPDN subgroups by using either the request dialin or request dialout command.
A LAC configured to request dial-in can be configured with multiple initiate-to commands to tunnel to more than one IP address.
An LNS configured to request dial-out can be configured with with multiple initiate-to commands to tunnel to more than one IP address.
Examples
The following example configures VPDN group 1 to request an L2TP tunnel to the peer at IP address 10.3.2.1 for tunneling dial-out calls from dialer pool 1. This group can tunnel a maximum of five simultaneous users and it has the second highest priority for requesting dial-out calls.
vpdn-group 1request-dialoutprotocol l2tppool-member 1initiate-to ip 10.3.2.1 limit 5 priority 2The following example configures VPDN group 1 to request L2TP tunnels to the peers (LACs) at IP addresses 10.0.58.201 and 10.0.58.205. The two LACs configured by the initiate-to commands have differing priority values to provide failover redundancy.
vpdn-group 1accept-dialinprotocol l2tpvirtual-template 1request-dialoutprotocol l2tppool-member 1initiate-to ip 10.0.58.201 priority 1initiate-to ip 10.0.58.205 priority 100source-ip 10.0.58.211In the previous example, you would configure load balancing among the LACs by setting the priority values in the initiate-to commands to the same values.
The following partial example shows how to set parameters to control how many times an LNS will retry connecting to a LAC, and the amount of time after which the LAC will declare itself down or busy so that the LNS will try connecting to the next LAC. (Note that the l2tp tunnel commands are optional and should be used only if it becomes necessary to change the default settings for these commands.)
!vpdn enablevpdn search-order domain!vpdn-group 1...request-dialoutprotocol l2tppool-member 1initiate-to ip 10.0.58.201 priority 1initiate-to ip 10.0.58.207 priority 50initiate-to ip 10.0.58.205 priority 100l2tp tunnel retransmit initial retries 5l2tp tunnel retransmit initial timeout min 4l2tp tunnel busy timeout 420...Related Commands
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