2960x and PoE+

[CrackedJack1]

I've got some cameras that need PoE+ and with the default config, the 2960x doesn't seem to deliver the power needed (another sg300 and netgear that I tried work fine with their defaults). Nothing I tried worked until I turned on LLDP (lldp run) and then the cameras were getting enough power to work. Is what I did correct or is there another solution that would be better? Is there any issue with having LLDP on?

After I got the cameras working, I noticed that the 2960x was taking the full 30W out of its budget for the cameras instead of just what they are currently asking for like other smaller desktop switches I've checked seem to do. Is there a command to make the switch allocate just what the camera wants as opposed to giving it the full 30 and having half of that go unused?

Thanks

[Leo Laohoo]

Is what I did correct or is there another solution that would be better? Is there any issue with having LLDP on?

Some devices do not support Cisco CDP.  Cisco CDP is the protocol used by Cisco switches to negotiate how much power is needed. 

Is there a command to make the switch allocate just what the camera wants as opposed to giving it the full 30 and having half of that go unused?

Use the interface command "power inline static <VALUE>" to assign specific amount of power the port will provide.

[CrackedJack1]

Hi Leo,

I don't want to assign a specific amount of power to a port.

On some small 8 port switches I've used (Cisco, HP and NetGear), they seem to deduct only the actual power used by the device from the available power on the switch, not what the class says it can use.

For example, suppose a class 4, 30W device is being reported by the switch as consuming 10W (and the switch still correctly sees it as a class 4 device). If the switch can supply up to 60W total, it will report I have 60-10=50W available.

The 2960x seems to be doing 60-30=30W available. How can I make the 2960x only account for the power currently used (ie. 60-10=50) instead of the maximum for the class?

[Kevin-John Beasley]

As per Leo's comment, these devices don't support CDP to negotiate their power usage so as soon as they need more than 15.4W (which they communicate using LLDP so yes you were correct and have to have that turned on) the switch puts the ports in high power mode and they get the full 30W per port. There is no way for the device to communicate or for the switch to determine what power is actually needed so the output and therefore allocation has to be 30W per port. AFAIK there is no way that a non-CDP device will ever show up as not using the full power requirement of their class.

That said I haven't tried but just saw the following:

lldp tlv-select power-management - Enables LLDP power negotiation. 

So maybe try that.

[CrackedJack1]

That lldp command is there by default I think. After I put in the command, it takes it but the config doesn't show it so I think it's default.

I ended up opening a ticket with Cisco and basically they said the switch is operating as expected, nothing can be done.

It's still interesting, to me anyway, that an SG300 can correctly detect the power used by a couple of devices (one sends LLDP messages, one doesn't) while the 2960x can't. The example is from my ticket were I was using the same two devices and moving them between the switches:

Device 1: doesn't send LLDP messages:

SG300: class 0, reported as using 2.3 watts

2960x: class 0, reported as using 15.4 watts

Device 2: does sent LLDP messages:

SG300: class 4, reported as using 9.2 watts

2960x: class 4, reported as using 25.5 watts