HP StorageWorks Fabric OS 5.0.0 Command Reference Guide (AA-RW1MA-TE, May 2005)

Fabric OS 5.0.0 command reference guide 427
Configures a port to receive multicast frames.
Synopsis
portCfgMcastLoopback [slotnumber/]portnumber, mode
Availability
admin
Description
Use this command to allow 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/sec 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
are routed to that multicast loopback port where it is loopbacked to the port's receiver that is turned off.
This effectively sends the frames to a black hole. Since the embedded processor is not involved, traffic
moves at normal (and full) speed.
Executing this command on a branch (middle) switch does 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 flash memory and is persistent across switch reboot or power cycle. The
user is prompted the follow occurs:
• 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.
When a port is configured as multicast loopback port:
• Its port LED blinks a slow green indicating a loopback state. Its laser, if optical GBICed, is disabled. It
does not respond to any attempt to connect it to any device.
• The comment field of switchShow displays that it is looped back to itself such as:
port 3: sw No_Light Loopback->3
• The portFlags line of portShow displays the F_PORT and INT_LB flags such as:
portFlags: 0x20249 PRESENT F_PORT U_PORT INT_LB LED
Operands
The operands are as follows:
portCfgMcastLoopback
slotnumber Specifies the slot number for a Core Switch 2/64 or SAN Director
2/128. For all other switches, this operand is not required. The slot
number must be followed by a slash (/) and the port number.
The Core Switch 2/64 and SAN Director 2/128 have a total of 10 slots.
Slot numbers 5 and 6 are control processor (CP) cards, and slots 1
through 4 and 7 through 10 are port cards. There are 16 ports on each
port card, counted from the bottom up, 0 to 15.
portnumber Specifies a port number. Valid values for port number vary. depending
on the switch type. This operand is required.