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Remote Loopback for Link Fault Management

 

Use this topic to understand what happens when you set a remote interfaces in loopback mode and how to enable remote loopback. You can also learn how to enable nonstop routing for LFM.

Setting a Remote Interface into Loopback Mode

You can configure the software to set the remote DTE into loopback mode on the following interfaces:

  • IQ2 and IQ2-E Gigabit Ethernet interfaces

  • Ethernet interfaces on the MX Series routers or EX Series switches

Junos OS can place a remote DTE into loopback mode (if remote-loopback mode is supported by the remote DTE). When you place a remote DTE into loopback mode, the interface receives the remote-loopback request and puts the interface into remote-loopback mode. When the interface is in remote-loopback mode, all frames except OAM PDUs are looped back without any changes made to the frames. OAM PDUs continue to be sent to the management plane and processed.

To configure remote loopback, include the remote-loopback statement at the [edit protocol oam ethernet link-fault-management interface interface-name] hierarchy level:

To take the remote DTE out of loopback mode, remove the remote-loopback statement from the configuration.

Enabling Remote Loopback Support on the Local Interface

You can allow a remote DTE to set a local interface into remote loopback mode on IQ2 and IQ2-E Gigabit Ethernet interfaces and all Ethernet interfaces on the MX Series routers and EX Series switches. When a remote-loopback request is sent by a remote DTE, the Junos OS places the local interface into loopback mode. When an interface is in loopback mode, all frames except OAM PDUs are looped back without any changes to the frames. OAM PDUs continue to be sent to the management plane and processed. By default, the remote loopback feature is not enabled.

To enable remote loopback, include the allow-remote-loopback statement at the [edit protocol oam ethernet link-fault-management interface interface-name negotiation-options] hierarchy level:

Note

Activation of OAM remote loopback may result in data frame loss.

Starting in Junos OS Release 17.3R1, the Ethernet link fault management daemon (lfmd) runs on the backup Routing Engine as well when graceful Routing Engine switchover (GRES) is configured. When the lfmd daemon runs on the backup Routing Engine as well, the link fault management states are kept in sync and so minimal effort is required by the lfmd daemon post switch over.

To enable Nonstop routing for Ethernet LFM on backup routers:

  1. Enable graceful Routing Engine switchover. By default, GRES is disabled. To enable GRES, include the graceful-switchover statement at the [edit chassis redundancy] hierarchy level. By default, Nonstop routing is disabled. When you enable GRES, NSR is enabled.
  2. Synchronize the Routing Engine configuration. To synchronize the master Routing Engine configuration with the backup, include the synchronize statement at the [edit system] hierarchy level.
  3. After enabling nonstop routing, commit the configuration.
  4. To verify if nonstop routing is enabled on the backup router, at the operational mode, use the show oam ethernet link-fault-management command on the master router and then the backup router. Because you have enabled synchronization, the output of the master router and the backup router is identical. However, the statistics maintained by the master router are not synchronized with the backup router..
    Note

    After the switchover, if issues are observed, use the clear oam ethernet link-fault-management state command for specific sessions. If the issue does not get resolved, restart the lfmd daemon.

Example: Configuring Ethernet LFM with Loopback Support

In this example, LFM is configured between provider edge (PE) router and the customer edge (CE) router. The PE router can put the CE router in remote loopback mode. This allows the PE to have all the traffic sent to the CE router looped back for diagnostics purposes, as shown in Figure 1.

Figure 1: Ethernet LFM with Loopback Support
Ethernet LFM with Loopback Support

To configure LFM between a PE router and a CE router:

  1. Configure LFM loopback on the PE router:

  2. Configure LFM loopback on the CE router:

    Note

    If the negotiation options allow-remote-loopback statement on the CE router is deleted before removing the CE router from remote loopback mode, traffic flow between the PE router and CE router is affected. Hence, delete the remote-loopback statement on the PE router before deleting the negotiation-options allow-remote-loopback statement on the CE router.

Release History Table
Release
Description
Starting in Junos OS Release 17.3R1, the Ethernet link fault management daemon (lfmd) runs on the backup Routing Engine as well when graceful Routing Engine switchover (GRES) is configured.