IMC Networks iMcV-Giga-FiberLinX-II - Manual (Page 16)

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Loopback Testing on Remote or Standalone
The following functions are available during loopback testing. During loopback
testing, management traffic entering the uplink port is still capable of managing the
device.
Address Swap
A Layer 2 Ethernet switch will discard all received packets with the same MAC
address as sent packets. To avoid this issue the Loopback feature can swap the
source and destination MAC addresses on the looped data.
Address Swap and Clear Multicast Bit
In addition to swapping the source and destination MAC addresses on the looped
data, the Loopback feature can also be set to clear the multicast bit. This allows the
looped data to avoid being blocked by any multicast settings.
No Learning on OPTICS and DATA Ports
The Loopback feature can be set to disable address learning on the OPTICS (or
UPLINK) and DATA ports, allowing the loopback to be performed without
interference from MAC address filtering functions. This is a function on the HOST
unit. Set the REMOTE unit for Loopback then set the HOST to disable learning so
Loopback frames pass from the OPTICS port to the DATA port.