Table Of Contents
L2TP Dial-Out Load Balancing and Redundancy
The L2TP Dial-Out Load Balancing and Redundancy feature introduces the ability to configure a tunnel server with the IP addresses of multiple network access servers (NASs). You can control load balancing, redundancy, and failover for Layer 2 Tunnel Protocol (L2TP) virtual private dialup network (VPDN) calls by assigning each NAS the desired priority settings on the tunnel server. Load balancing occurs between NASs with identical priority settings. When NASs are assigned different priority settings, if the NAS with the highest priority goes down the tunnel server will fail over to a lower priority NAS.
Configuration information is included in the "Configuring Additional VPDN Features" module of the Cisco IOS VPDN Configuration Guide, Release 12.4T, at the following URL:
This section documents modified commands.
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 virtual private dialup network (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]
No IP address is specified.
VPDN group configuration
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 NAS configured to request dial-in can be configured with multiple initiate-to commands to enable tunneling to more than one IP address.
A tunnel server configured to request dial-out can be configured with multiple initiate-to commands to enable tunneling to more than one IP address.
The following example configures a VPDN group for L2TP dial-out. This group can tunnel a maximum of five simultaneous users and has the second highest priority for requesting dial-out calls.vpdn-group 1request-dialoutprotocol l2tppool-member 1!initiate-to ip 10.3.2.1 limit 5 priority
The following example configures VPDN group 1 to request L2TP tunnels to the peers (NASs) at IP addresses 10.0.58.201 and 10.0.58.205. The two NASs configured by the initiate-to commands have differing priority values to provide failover redundancy.vpdn-group 1accept-dialinprotocol l2tpvirtual-template 1!request-dialoutprotocol l2tppool-member 1!initiate-to ip 10.0.58.201 priority 1initiate-to ip 10.0.58.205 priority 100source-ip 10.0.58.211
In the previous example, you would configure load balancing among the NASs 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 a tunnel server will retry connecting to a NAS, and the amount of time after which the NAS will declare itself down or busy so that the tunnel server will try connecting to the next NAS. (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 1!initiate-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...