Chapter 12 Practical Cases; Backup Link In A Cisco Router With L2Tp - Teldat -3Ge-USB User Manual

12 Practical Cases

Chapter 12 Practical Cases

In this section we are going to discuss some practical cases regarding configurations in a real scenario. These cases
outline problems that may arise during configuration and ways that they can be solved.

12.1 Backup link in a Cisco router with L2TP

Configures the link through the Teldat-3Ge-USB as a backup link for another main link.
Note
This only applies if you are using L2TP, not PPPoE.
A Cisco router, on deactivating the backup link, does not negotiate PPP session closure with the network. Con-
sequently, we have to add to the configuration, to resolve this, so the Teldat-3Ge-USB understands the Cisco router
has dropped the link. The Teldat-3Ge-USB subsequently needs to release communication with the mobile telephony
carrier network. If we don't do this, the Teldat-3Ge-USB remains permanently connected.
To detect a drop in the PPP link, use a Cisco feature known as EEM ( Embedded Event Manager). and monitor for a
Virtual-ppp interface drop. When this occurs, execute a clear for all the L2TP tunnels so the session and the L2TP
tunnel established with the Teldat-3Ge-USB both drop. When the L2TP tunnel goes down, the Teldat-3Ge-USB re-
leases the PPP link and disconnects from the mobile network.
The commands to add are as follows:
• To make the Virtual-ppp interface become the backup link for the other interface, add the following command in the
main interface configuration:
backup interface Virtual-ppp1
• To ensure the link with the mobile network is released on return from backup:
If the Cisco router has an IOS later or equal to 12.4.15.
!
event manager applet ETHANT-DOWN
event syslog pattern "Interface Virtual-PPP1, changed state to standby mode"
action 1.0 cli command "enable"
action 1.1 cli command "clear vpdn tunnel l2tp all" pattern "confirm"
action 1.2 cli command "y"
action 1.3 cli command "exit"
!
If the Cisco router has an IOS prior to 12.4.15.
!
event manager applet ETHANT-DOWN
event syslog pattern "Interface Virtual-PPP1, changed state to down"
action 1.0 cli command "enable"
action 1.1 cli command "conf te"
action 1.2 cli command "interface virtual-ppp1"
action 1.3 cli command "no pseudowire"
action 1.4 cli command "pseudowire 1.1.1.2 1 pw-class pwclass1"
action 1.5 cli command "exit"
action 1.6 cli command "exit"
action 1.7 cli command "exit"
!
Note
You must substitute the interfaces and the IP addresses for the appropriate ones in each case.
We recommend you check that the specific IOS DEBUG messages for the Cisco router coincide with
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