Using 802.1ag MAC Trace to Monitor the Forwarding Path on a Layer 2 Network

802.1ag MAC trace monitors the connectivity between MEPs or between MEPs and MIPs within an MA and provides information used to locate faults.

Context

Similar to traceroute or tracert, 802.1ag MAC trace tests the path between the local device and a destination device or locates failure points by sending test packets and receiving reply packets.

Before performing 802.1ag MAC trace, ensure that 802.1ag has been configured. For more information, see Configuring Basic Ethernet CFM Functions.

Procedure

A device is usually configured with multiple MDs and MAs. To determine the forwarding path for sending packets from a MEP to another MEP or a MIP in an MA or failure points, perform either of the following operations on the router with a MEP at one end of the link to be tested.
- In the MA view:
  1. Run system-view
    The system view is displayed.
  2. (Optional) Run cfm portid-tlv type { interface-name | local }
    The portid-tlv type for trace packets is set.
  3. Run the cfm enable command to globally enable the CFM function on the device.
  4. Run cfm md md-name
    The MD view is displayed.
  5. Run ma ma-name
    The MA view is displayed.
  6. Run the trace mac-8021ag mep mep-id mep-id [ md md-name ma ma-name ] { mac mac-address | remote-mep mep-id mep-id } [ -t timeout | ttl ttl ] ^* command to locate the connectivity fault between the local and peer devices.
    - Run the trace mac-8021ag command without md md-name ma ma-name in the MA view to monitor a forwarding path or locate a failure point in the current MA.
    - Run the trace mac-8021ag md md-name ma ma-name command in the MA view to monitor a forwarding path or locate a failure point in the specified MA.
      
      An example is as follows:
```
<HUAWEI> system-view 
[~HUAWEI] cfm enable
[*HUAWEI] cfm md md1 
[*HUAWEI-md-md1] ma ma1 
[*HUAWEI-md-md1-ma-ma1] trace mac-8021ag mep mep-id 1 md md1 ma ma1 remote-mep mep-id 8
Tracing the route to 00e0-fc12-3458 over a maximum of 64 hops: 
 Hops  Ingress Mac    Ingress Port                Ingress Action    Relay Action
       Egress Mac     Egress Port                 Egress Action     Ismep 
 1     00e0-fc23-3459 GigabitEthernet0/1/1        IngOK             RlyFDB
       00e0-fc22-3459 GigabitEthernet0/1/2        EgrOK             NoMep 
 2     --             --                          --                RlyHit
       00e0-fc12-3458 GigabitEthernet0/1/3        EgrOK             IsMep 
Info: Succeeded in tracing the destination address 00e0-fc12-3458. 
```
- In all views except the MA view:
  1. (Optional) Run cfm portid-tlv type { interface-name | local }
    The portid-tlv type for trace packets is set.
  2. Run trace mac-8021ag mep mep-id mep-id md md-name ma ma-name { mac mac-address | remote-mep mep-id mep-id } [ -t timeout | ttl ttl ] *
    The connectivity fault between the local and the remote devices is located.
When implementing 802.1ag MAC trace, ensure that:
- The MEP is configured in the MA.
- If the outbound interface is specified, no inward-facing MEP is configured on it. The interface must be added to the VLAN associated with the MA.
- If the destination node is an RMEP, either mac mac-address or remote-mep mep-id mep-id can be selected. If remote-mep mep-id mep-id is selected, the RMEP must already be created using the remote-mep command.
- If the destination node is a MIP, select mac mac-address.
- If the forwarding entry of the destination node does not exist in the MAC address table, interface interface-type interface-number must be specified.
(Optional) Run display cfm statistics lblt
802.1ag protocol packet statistics are displayed.

If the test using the trace mac-8021ag command fails, you can run this command to check whether a link fault or a device fault occurs.
(Optional) Run reset cfm statistics lblt
The 802.1ag protocol packet statistics are displayed.