The loopback function is supported by 802.1ag and Y.1731 on the 7705 SAR. A Loopback Message (LBM) is generated by a MEP to its peer MEP. Both dot1ag and dot3ah loopbacks are supported. The loopback function is similar to IP or MPLS ping in that it verifies Ethernet connectivity between the nodes on a per-request basis. That is, it is non-periodic and is only initiated by a user request.
In Figure: Dot1ag Loopback Test, the line labeled LB represents the dot1ag loopback message between the 7750 SR (source) and 7705 SAR (target) over an Ethernet PW (Epipe). The 7750 SR-generated LBM is switched to the 7705 SAR, where the LBM is processed. After the 7705 SAR generates the Loopback Reply message (LBR), the LBR is switched over the Epipe to the 7750 SR.
ETH-LB tests are run using the oam>eth-cfm>loopback command.
