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Example: L2TP LNS CoS Support for Link Redundancy

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

Note: 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.

Requirements

• 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.

Overview

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 192.168.100.0 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 CoS

Configuration

Step-by-Step Procedure

1. Configure Gigabit Ethernet interfaces.
   [edit interfaces]user@host# set ge-0/3/1 unit 0 family inet address 192.168.1.1/30user@host# set ge-0/3/3 unit 0 family inet address 192.168.1.5/30user@host# set ge-0/3/1 unit 0 per-session-scheduleruser@host# set ge-0/3/3 unit 0 per-session-scheduler
2. Configure static routing options.
   [edit routing-options]user@host# set static route 192.168.100.0/24 next-hop [ 192.168.1.2 192.168.1.6 ]

Step-by-Step Procedure

1. Verify that LAC is reachable.
   user@host> show route 192.168.100.1

   inet.0: 14 destinations, 14 routes (14 active, 0 holddown, 0 hidden)
   + = Active Route, - = Last Active, * = Both
   
   192.168.100.0/24   *[Static/5] 1d 02:09:09
                         to 192.168.1.2 via ge-0/3/1.0
                       > to 192.168.1.6 via ge-0/3/3.0
   

2. Bring up an L2TP session and verify that L2TP sessions come up.
   user@host> show services l2tp session

   Interface: sp-1/3/0, Tunnel group: GEN-TUN-GRP-BIO, Tunnel local ID: 44806
     Local Remote Interface State               Bundle Username
     ID    ID     unit
     12491  33795         1 Established              - test1
   

3. Send a traffic stream towards the subscriber.
4. Verify that the shaping at the subscriber end is as per the shaping rate configured.
   user@host# show class-of-service l2tp-session

   L2TP Session Username: test1, Index: 12491
   Physical interface: ge-0/3/3, Index: 131
   Queues supported: 4, Queues in use: 4
     Scheduler map: GEN-SCHED-MAP-EF-65%, Index: 5212
     Shaping rate: 2162200 bps
     Encapsulation Overhead: 6, Cell Overhead: Enabled
   

   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.

Verification

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
• Verify LAC Reachability and the Status of L2TP Sessions

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

Purpose

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

Action

Verify LAC Reachability and the Status of L2TP Sessions

Purpose

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.

Action

inet.0: 14 destinations, 14 routes (14 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

192.168.100.0/24   *[Static/5] 1d 02:35:09
                      to 192.168.1.2 via ge-0/3/1.0
                   

Interface: sp-1/3/0, Tunnel group: GEN-TUN-GRP-BIO, Tunnel local ID: 44806
  Local Remote Interface State               Bundle Username
  ID    ID     unit
  12491  33795         1 Established              - test1