Fabric OS Reference Manual

152 Fabric OS Reference Manual
portcfgMcastLoopback
Configure a port to receive multicast frames.
Synopsis
portCfgMcastLoopback portnumber, 0|1
Availability admin
Description Use this command to configure a port to receive multicast frames. This
command allows a user to dedicate an unused port in a leaf (edge) switch,
with no F_Port belonging to a multicast group, to receive multicast frames.
When multicast frames are received at an edge switch with no member
port, traffic will throttle down in the KBytes/Second range as embedded
processor intervention is required to process it.
However, when a port is assigned as the multicast loopback port, frames
destined for any multicast group will be routed to that multicast loopback
port where it is loopbacked to the port’s receiver, which is turned off. This
effectively sends the frames to a black hole. Since an embedded processor
is not involved, traffic moves at normal (and full) speed.
Executing this command on a branch (middle) switch will not affect traffic.
It can be configured for future use as an edge switch. The disadvantage is
that the port cannot be used to connect to other devices.
The configuration is saved in the non-volatile memory and is persistent
across switch reboot or power cycle.
The user will be prompted under two circumstances:
• The selected port is already in use as an E_Port, or Fx_Port.
• The switch is a branch (middle) switch.
A warning message is printed if another port is already configured as the
multicast loopback.