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Beginner

What does "power inline port 2x-mode" really do?

I have seen this command in multiple forum posts and it does help in a lot of PoE siutations. But nowhere could i find information that explains what this command does in more detail. It iosn't even mentioned in the troubleshoting PoE guide:

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/troubleshooting/g_power_over_ethernet.html

We have some PoE devices in our network, that rely on this command to be configured on the interface in order to power up. Because we want IT staff to be able to patch all equipment on every port of the switch, we'd like to roll out the command power inline port 2x-mode on every interface on all switches. Question: Does this command cause any harm to NonPoE or PoE devices that dont rely on it?

Is there any impact to be expected? I know that the power inline static command can cause damage since the port is always giving out 100%.

Is there any official cisco documentation explaining this command in more detail?

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VIP Expert

There isn't on official Cisco

There isn't on official Cisco doc explaining it but it appears that the command is used when connecting 3rd party vendor deices to Cisco switches.  Here is another post that explains the use of it:

https://supportforums.cisco.com/discussion/11447341/3750-switch-marking-shoretel-poe-phones-faulty

Also, it seems as this command is no longer available in newer platforms i.e 3650, 3850 with newer IOS versions.

HTH

Highlighted
Beginner

Thank you for the link. In

Thank you for the link. In there, somone explains, that with this command, the port is able to withstand peaks that are out of specification:

implemented this power inline 2x-port mode method to handle devices which spike the current like this but don't actually fall out of the IEEE 802.3af spec.  The momentary spike is out of spec, but the power is measured as an average and the average doesn't fall out of spec (though it's close). 

This would explain why longer cables would fix the problem as well. The spikes would then be  weakend by the cable loss and not fall outside of specifications anymore.

Highlighted
Beginner

Re: There isn't on official Cisco

The command power inline port 2x-mode is available on the 3650 with version 16.3.7

 

Cheers!

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Hall of Fame Community Legend

Question: Does this command

Question: Does this command cause any harm to NonPoE or PoE devices that dont rely on it?

Yes and no. 

When a powered device (PD) starts up, rules (and common sense) states that the PoE port will dish out 15.4w (even though the PD uses <15.4w).  The logic behind this is that during the boot-up of the PD there is no way to tell how much power the device will use/require.  It's only when the PD starts talking will it up-shift or down-shift the power and negotiate. 

Now during this stage the PD is getting the full 15.4w power and this doesn't fry the components inside. 

Now I'm saying that this will with current generation.  It all depends on the manufacturer of the PD if they built the PD with the correct (standards) or code it correctly or not.  Hence, my answer of "yes and no".  

With Cisco gear, I know they can tolerate the discrepancies but I don't know the rest.

Highlighted
Beginner

Thank you for your answer. I

Thank you for your answer. I did some testing with this 2x-mode command. I cannot confirm that the port is pushing 15.4W while the PD starts. Maybe i just couldnt see it. I tested following devices:

Device                       Power on Boot       Power on Operation

Alcatel DECT antenna         7W                  7W

Panasonic camera             4W                  4W

Panasonic camera (outside)   15.4W               15.4W

Cisco AP 2602I               15.4W               15.4W

Cisco AP 1242AG              15.4W               15.4W

Cisco AP 2802I               15.4W               26.1

Cisco AP 1532I               15.4W               30W

Cisco AP 1562I               15.4W               29.9W

The startup behaviour was exactly the same with and without the 2x-mode command on every device. Expect for the AP 1562 that does not come up without this command. It just keeps on rebooting while only draining 15.4W from the switchport.

So as far as i tested it is save to have this command enabled on all of the interfaces in our environment. I will report back here if i encounter any broken PoE device that could have been caused by this command.

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Hall of Fame Community Legend

Expect for the AP 1562 that

Expect for the AP 1562 that does not come up without this command.

I believe this command is hardware-specific to the 2960X only.  I have tried plugging a 1562I into a 2960S and 3560CG and, even though both units support up to 30.0w PoE, the AP came up fine.  

I find the behaviour of the 2960X to be a bit "odd" in some cases.  I have a large fleet of 2960S but a few 2960X and I never had any significant issues with the 2960-family of switches (including 2960S and 2960X) but this undocumented command is indeed strange.  

NOTE:  1562I requires 32.0w PoE on paper but actually requires 39.9w PoE.  

Highlighted
Beginner

Thank you for your time to

Thank you for your time to reply. As of your comment:

NOTE:  1562I requires 32.0w PoE

Thats what i always didnt understand. Specification tells that the Switch can send out max 30W. Usually somewhere between 25 and 27W arrive at the PD. Rest is lost due to cabling resistance. So i dont get the 32W requirement and then saying 802.3at is enough for the device to be powered.

Due to the lack of documentation about this, i thought only additional testing would bring light into this dark matter. And so i did. I connected the 1562I to a 3850 UPoE Switch. This is the Cisco propriotary thing that they do before 802.3bt comes out. No special config on the switchport. During boot, the AP drains the usual:

swRZ101(config-if)#do show power inline gig 3/0/30
Interface Admin  Oper       Power   Device              Class Max
                            (Watts)                            
--------- ------ ---------- ------- ------------------- ----- ----
Gi3/0/30  auto   on         15.4    Ieee PD             4     60.0

But after it completed booting up, there is now a value that i've never seen before:

swRZ101(config-if)#do show power inline gig 3/0/30
Interface Admin  Oper       Power   Device              Class Max
                            (Watts)                            
--------- ------ ---------- ------- ------------------- ----- ----
Gi3/0/30  auto   on         39.1    AIR-AP1562I-E-K9    4     60.0

After completing setup and using dual band, the access point drains almost 40W. I checked the access point PoE Status. It says Full Power.

So this access point left me puzzled in many ways. Hopefully Cisco will fix some of this behaviour with firmware updates in the future.

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Hall of Fame Community Legend

Whao!  39.1w????  That's not

Whao!  39.1w????  That's not what is in the Data Sheet!

Can I ask if you can raise this issue with TAC?  I think this is a bug with the 3850.

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