Guidelines for Starting an ETH-DM Session

Keep the following guidelines in mind when preparing to start an Ethernet frame delay measurement (ETH-DM) session:

• ETH-DM Session Prerequisites
• ETH-DM Session Parameters
• Restrictions for an ETH-DM Session

ETH-DM Session Prerequisites

Before you can start an ETH-DM session, you must configure two MX Series routers to support ETH-DM by defining the two CFM-enabled physical or logical Ethernet interfaces on each router. This entails creating and configuring CFM maintenance domains, maintenance associations, and maintenance association end points on each router. For more information about enabling CFM on an Ethernet interface, see Creating the Maintenance Domain.

Note: The Ethernet frame delay measurement feature is supported only for maintenance association end points configured on Ethernet physical or logical interfaces on DPCs in MX Series routers. The ETH-DM feature is not supported on aggregated Ethernet interfaces or LSI pseudowires.

For specific information about configuring routers to support ETH-DM, see Guidelines for Configuring Routers to Support an ETH-DM Session and Configuring Routers to Support an ETH-DM Session.

ETH-DM Session Parameters

You can initiate a one-way or two-way ETH-DM session by entering the monitor ethernet delay-measurement operational command at a router that contains one end of the service for which you want to measure frame delay. The command options specify the ETH-DM session in terms of the CFM elements:

• The type of ETH-DM measurement (one-way or two-way) to be performed.

• The Ethernet service for which the ETH-DM measurement is to be performed:

  • CFM maintenance domain—Name of the existing maintenance domain (MD) for which you want to measure Ethernet frame delays. For more information, see Creating the Maintenance Domain.
  • CFM maintenance association—Name of an existing maintenance association (MA) within the maintenance domain. For more information, see Creating a Maintenance Association.
  • Remote CFM maintenance association end point—The unicast MAC address or the numeric identifier of the remote maintenance association end point (MEP)—the physical or logical interface on the remote router that resides in the specified MD and is named in the specified MA—with which to perform the ETH-DM session. For more information, see Configuring a Maintenance Endpoint and Configuring a Remote Maintenance End Point.

• Optional specifications:

  • Count—You can specify the number of ETH-DM requests to send for this frame delay measurement session. The range is from 1 through 65,535 frames. The default value is 10 frames.

    NOTE: Although you can trigger frame delay collection for up to 65,535 ETH-DM requests at a time, a router stores only the last 100 frame delay statistics per CFM session (pair of peer MEPs).

  • Frame interval—You can specify the number of seconds to elapse between ETH-DM frame transmittals. The default value is 1 second.

For more detailed information about the parameters you can specify to start an ETH-DM session, see the monitor ethernet delay-measurement operational command description in the JUNOS System Basics and Services Command Reference.

Restrictions for an ETH-DM Session

The following restrictions apply to an ETH-DM session:

• You cannot run multiple simultaneous ETH-DM sessions with the same remote MEP or MAC address.
• For a given ETH-DM session, you can collect frame delay information for a maximum of 65,535 frames.

• For a given CFM session (pair of peer MEPs), the ETH-DM database stores a maximum of 100 statistics, with the older statistics being “aged out” as newer statistics are collected for that pair of MEPs.

  • For one-way delay measurements collected within the same CFM session, the 100 most recent ETH-DM statistics can be retrieved at any point of time at the router on which the receiver MEP is defined.
  • For two-way delay measurements collected within the same CFM session, the 100 most recent ETH-DM statistics can be retrieved at any point of time at the router on which the initiator MEP is defined.
  Depending on the number of frames exchanged in the individual ETH-DM sessions, the ETH-DM database can contain statistics collected through multiple ETH-DM sessions.
• If graceful Routing Engine switchover (GRES) occurs, any collected ETH-DM statistics are lost, and ETH-DM frame counts are reset to zeroes. GRES enables a router with dual Routing Engines to switch from a master Routing Engine to a backup Routing Engine without interruption to packet forwarding. For more information, see the JUNOS High Availability Configuration Guide.
• Accuracy of frame delay data is compromised when the system is changing (such as from reconfiguration). We recommend performing Ethernet frame delay measurements on a stable system.

Related Topics

• Ethernet Frame Delay Measurements Overview
• Starting an ETH-DM Session
• Guidelines for Managing ETH-DM Statistics and ETH-DM Frame Counts
• monitor ethernet delay-measurement operational command