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Problem: any sleeping computer on a gigabit network causes all multicast traffic to drop to 10Mbps.

Solution: provide customers with managed gigabit switches and train them to configure the switches manually. Not an ideal solution.

I discovered today another workaround… the cause is 802.3x flow-control. Disabling flow-control fixes the problem: 

sudo ifconfig en0 -mediaopt flow-control

However this means that every device on every customers network would need to turn off auto negotiation, then manually turn flow-control off. Turning off auto-negotiation is a very bad idea. Not a workable solution.

One example: I notice that on my dumb, old gigabit switch,

  • sleeping machine has flow control ON , link light ON, 1000Mbps light is off
  • sleeping machine has flow control OFF, link light ON, 1000Mbps light is lit.

My question is: Is there any RFC/protocol which would allow traffic to ignore flow-control. (Probably not)

Is there any RFC/protocol/hack to discover whether a sleeping device on a network uses flow-control… (Maybe?)

Is there any RFC/protocol/hack to discover what is the auto-negotiated speed of each device on its immediate switch (albeit dumb switch)?

This would at least allow my software to warn a user why their multicast performance is 10Mbps.

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My question is: Is there any RFC/protocol which would allow traffic to ignore flow-control. (Probably not)

Ethernet is not controlled by the IETF RFCs, it is from the IEEE 802.3 committee. Many devices do ignore ethernet flow control; it is poorly supported, and it is not required. Even among network devices which do support it, you must often enable it.

Is there any RFC/protocol/hack to discover whether a sleeping device on a network uses flow-control… (Maybe?)

Sleeping devices don't tell you anything; you must first wake them. Hosts are off-topic here. There will be no RFC because the IETF doesn't deal with ethernet standards, and I know of no such protocol from the IEEE.

Is there any RFC/protocol/hack to discover what is the auto-negotiated speed of each device on its immediate switch (albeit dumb switch)?

If a switch or the host supports SNMP, then you could use SNMP to discover such things, but that is unlikely for a dumb switch.

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