---
title: "Set Up Loopback Messages"
slug: "setting-up-loopback-messages"
tags: ["loopback", "ECFM ", "MEP", "sensor control ", "Assurance Sensor Control"]
updated: 2026-07-07T13:58:25Z
published: 2022-02-25T20:22:35Z
canonical: "docs.crossworkassurance.cisco.com/setting-up-loopback-messages"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.crossworkassurance.cisco.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Set Up Loopback Messages

Loopback messages are unicast frames transmitted by a MEP. Sending a high volume of loopback messages can test the bandwidth, reliability or jitter of a service. A MEP can send a loopback to any MEP or MIP in the service. Loopback messages are discussed in IEEE 802.1ag.

**▶ To start the loopback messages**

1. Access the page **SOAM ▶ CFM ▶ MEP ▶ LBM**. All existing loopback messages for Maintenance association End Points are displayed.
2. Click the **MEPID** of the MEP for which you want to start the LBM.
3. Complete the required fields, then click **Start**.

For more information on specific parameters, refer to the following tables.

**MEP Loopback (SOAM ▶ CFM ▶ MEP ▶ LBM)**

| Parameter | Description |
| --- | --- |
| MEP Index Index | Index assigned to the Maintenance association End Point |
| MEPID | Maintenance association End Point Identifier |
| Active | Indicates whether a loopback request is active for that MEP |
| Target Type | Loopback target by remote MEPID, MAC address or Multicast |
| Remote MEPID | Target remote MEPID. The remote MEP MAC address is resolved into the local MEP database. |
| MAC Address | Target MAC address. Only Unicast MAC address are valid for link trace target address. |
| VLAN Priority | Indicates how to determine the LBM VLAN priority value: <UL**CCM Priority**: Use the same priority that MEP CCMs.**Specific**: Use a specific value specified by the Priority field. |
| Priority | The value assigned to the LBM VLAN priority Range: 0-7 |
| VLAN Drop Eligibility | Value for LBM VLAN drop eligibility bit. Checking this box sets the DEI bit to 1. |
| Nbr Message | Number of LBMs to send |
| Interval | The interval, expressed in milliseconds, between LBMs Range: 100–5000 |
| Data TLV | Indicates whether LBMs should include a Data Type Length Value (TLV). Possible values are: - **None**: No Data TLV included - **Incremental**: A Data TLV with incremental byte values is included. - **Pattern**: A Data TLV based on a user data pattern is included. |
| Length | Amount of data, expressed in bytes, inside the data TLV Range: 1–1488 bytes |
| Pattern | User data pattern for the Data TLV Format: ASCII characters |

**Bottom of Table**

| Parameter | Description |
| --- | --- |
| Loopback Request | Indicates whether a loopback request is **active** or **inactive** for that MEP |
| Target MAC Address | The target MAC address used for the latest loopback request |
| Latest Start Time | The time the latest loopback request was initiated for that MEP |
| Latest End Time | The time the latest loopback request has completed or was stopped for that MEP |
| Next Seq. # | The sequence number for the next LBM initiated from that MEP |
| Nbr LBM Requested LBM Requested | The number of LBM requested for the latest loopback request |
| Nbr LBM Sent | The number of LBM sent for the latest loopback request. When the loopback is not active, this number should be the same as the number of LBM requested. If not, this implies the loopback request was stopped by a management command. |
| Nbr LBR Received LBM Received | The number of loopback replies (LBR) received for the latest loopback request |
| LBR with Bad MSDU | The number of LBR received with a content that did not match the corresponding LBM for the latest loopback request |
| Nbr LBR Duplicated | The number of LBR received with a sequence number already received for the latest loopback request |
| Packet loss ratio | The computed packet loss ratio for the latest loopback request |
| Nbr Packet Lost | The number of missing LBR for the latest loopback request |
| Nbr Gaps | The number of times a sequence of LBRs went missing during the latest loopback request |
| Largest Gap Size | The longest uninterrupted sequence of missing packets that was detected during the most recent loopback request |
| Nbr LBR Out of Order | The number of times an LBR was received during the latest loopback request whose sequence number did not match the expected value |

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