Catalyst 9300-48U and “Power Inline 2-event”

[Badger-Fi]

I have read some resources concerning various devices needing “power inline 2-event” configured on ports that they are connected to and I am trying to understand the reasoning.

In my case I was having trouble with an Algo 8420 dual sided network clock not powering on when connected to a 9300-48U.  The switch has two 1100W power supplies which I see is required for UPOE+.  I get the same errors that others have seen in similar situations:

EST: %ILPOWER-3-CONTROLLER_PORT_ERR: Controller port error, Interface Gi3/0/4: Power given, but Power Controller does not report Power Good

Controller port error, Interface Gi3/0/4: Power Controller reports power Imax error detected

The 9300-48U in question is running IOS 17.03.04.

I can plug this same Algo clock into a generic unmanaged POE switch and a Meraki MS220 and it powers up and connects without issue.  When I configure “power inline 2-event” on the 9300-48U, the Algo 8420 does work.

My questions are these.  Are devices that are not LLDP capable the only devices that require this command to use 802.3bt?  If this Algo does not use LLDP to negotiate POE, why would the generic switch and/or Meraki MS220 work?  Basically, does this command only need to be applied on ports where PD devices that don’t use LLDP exist?

[Torbjørn]

PoE negotiation is either hardware based or hardware + software based. When a link is brought up between a Power Sourcing Equipment(PSE) and a Powered Device(PD) the PSE will send a voltage pulse to the PD and read the current that is drawn. This current will correspond to 1 of 5 classes(0-4). If it reads as class 4 the PSE will either supply a class 3 power and perform a second hardware classification(2-event classification) or it will perform software based classification(LLDP/CDP).

This is where "power inline 2-event" becomes relevant. Per 802.1at a PSE should support 2-event hardware negotiation _or_ software based negotiation while the PD should support both. When you enable "power inline 2-event" the switch will use the hardware based negotiation while the default is software based on catalyst switches.

power inline 2-event should hence only be applied on ports where devices that only supports hardware based/2-event negotiation are connected. I am not too familiar with Meraki switches, but I would assume that they either default to hardware based negotiation or detect failed negotiations and change the mode?

[Leo Laohoo]

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@Badger-Fi wrote:
I can plug this same Algo clock into a generic unmanaged POE switch and a Meraki MS220 and it powers up and connects without issue.  When I configure “power inline 2-event” on the 9300-48U, the Algo 8420 does work.

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This is a known issue/feature with switches that run IOS-XE.  

Cisco has made a mess with how PD that do not talk either CDP or LLDP gets power.  If the PD is plugged into a classic IOS, the PD will power up.  If the same PD is plugged into a switch that runs on IOS-XE, it is a coin-toss and may/may not work depending on the firmware version, uptime of the switch (not stack), the phase of the moon in correlation to the winning lotto ticket number.  

[Badger-Fi]

Thank you for the information.  I guess I am ok with making a non-standard configuration as long as there is good explanation.

Now that I have 2-event negotiation configured on the port and the device powers up, the issue is there is no data connection.  The link light doesn't come on.  If I run a TDR it shows pairs C and D as short.  If I plug the 8420 back into my Meraki switch, it still works perfectly.  I am assuming there is additional configuration that needs to take place.