23.1.5 Loopback
The loopback functionality can be used at the Layer 2 level, and is equivalent to pinging. The loopback function verifies the connectivity between MEPs or between a MEP and a MIP in the same MA.
The CC functionality verifies the connectivity between MEPs. The loopback functionality can additionally verify the connectivity between a MEP and a MIP, with the result that it can check the connectivity in an MA in greater detail.
Connectivity is verified by sending a loopback message (a kind of CFM PDU) from the MEP to the destination and confirming that the destination responds to the message.
The MIP or MEP responds directly to the loopback functionality. If, for example, multiple MIPs are configured on a switch, connectivity can be verified for each MIP.
The following figure shows an example of executing the loopback for MIPs and MEPs.
|
|
![[Figure Data]](./GRAPHICS/ZU219260.GIF)
|
|
![[Figure Data]](./GRAPHICS/ZU219270.GIF)
Because the loopback functionality uses what the CC functionality learns, the CC functionality must be started beforehand. If you configure a MIP on the destination switch, you must note the MAC address of the port used as the MIP beforehand.