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Example: Configuring L2TP LNS CoS Support for Link Redundancy

This example shows how link redundancy is supported when CoS for L2TP is configured on Ethernet interfaces.


In this example, support for link redundancy is demonstrated by manually disabling the interface. However, link redundancy is also supported when the interface goes down due to events such as disconnection of the cable or rebooting of the remote end system.


Before you begin:

  • Configure service and loopback interfaces.

  • Configure CoS for L2TP.

This feature applies to M Series Multiservice Edge Router running Junos OS Release 12.1 or later and EX Series switches.


Junos OS now supports link redundancy for CoS configured on an L2TP LNS. In this example, we verify that an L2TP tunnel does not go down when the Ethernet interface, through which the tunnels and its sessions with CoS are established, goes down.


Figure 1 shows a sample scenario in which L2TP access concentrator (LAC) devices operate on one side of an L2TP tunnel. LAC devices are configured with the address range of with a subnet mask of 24. The LAC devices are connected to two backbone routers, P1 and P2. These two routers, P1 and P2, are connected over two Gigabit Ethernet ports on a single Ethernet IQ2 PIC to an L2TP network server (LNS). The LNS device is a router running Junos OS that supports redundancy for terminating L2TP sessions configured with CoS parameters. The CoS settings are applied on the interfaces using a RADIUS server when the L2TP session is set up. One of the Gigabit Ethernet interfaces on the IQ2 PIC present on the LNS device, ge-0/3/1, is connected to P1, while the other interface, ge-0/3/3, is linked to P2. Such a method of connection enables the subscriber sessions that reach the LAC devices to be forwarded to one of the two ports of the IQ2 PIC on the LNS device.

Figure 1: Topology to Verify Link Redundancy Support for L2TP LNS CoSTopology to Verify Link Redundancy Support for L2TP LNS CoS



Step-by-Step Procedure

To configure Ethernet interfaces for redundancy:

  1. Configure Gigabit Ethernet interfaces.

  2. Configure static routing options.

Step-by-Step Procedure

Verify that CoS is now implemented over L2TP on an Ethernet interface and the LAC is reachable.

  1. Verify that LAC is reachable.

  2. Bring up an L2TP session and verify that L2TP sessions come up.

  3. Send a traffic stream towards the subscriber.

  4. Verify that the shaping at the subscriber end is as per the shaping rate configured.

    In the output of the show class-of-service l2tp-session command, ge-0/3/3, index 131 represents the port used to establish the L2TP tunnel to which the current L2TP session belongs. It does not represent the port that was active when the L2TP session came up.


Verify that, when CoS is configured on an L2TP tunnel, link redundancy works if one of the ports on which the L2TP tunnel is established goes down.

Bring Down ge-0/3/3 Interface Through Which the L2TP Tunnel Is Established


Bring down the interface through which the L2TP session and its tunnels are established.


Verify LAC Reachability and the Status of L2TP Sessions


Verify that link redundancy works and the L2TP session does not go down when the active port on the IQ2 PIC is down. Verify that the traffic flow is unaffected after it is switched to another port configured on the same IQ2 or IQ2E PIC.