CISCO 2960 Ethernet Link Disconnect

[KalpeshDiyora1281]

HI,

We are using diode oring on secondary of POE for Adaptor and TPS23753 output voltage(POE).

We have set adaptor priority by adjusting POE voltage less compare to Adaptor voltage.

In this case, POE is continuously disconnection due to less minimum load (MPS not maintained). Along with Power disconnect on POE line, CISCO 2960 switch disables Data from the line and our device(Product) went offline mode.

We have added minimum load on output of POE to Maintain the min load and problem get resolved.

We need to know below detail,

Why Switch disables Data along with power? Power disable is not effect our system configuration as adaptor power is present as secondary source.

SG300/SG350 not disables data when power disables due to MPS. We observed this issue with CISCO 2960 switch and customer end.

Can we do setting in switch configuration to overcome this issue?

[pieterh]

please read this post

My guess is: your setup with diodes interferes with the correct detection between 802.3af/at PoE and pre-standard PoE.

or the detection of power class does not function correctly.

after all the connected device is already powered from the other source

so the device may not give the right response on the PoE sequence from the switch , the switch remains in the power-detection phase and does not enable data

.

check with "show power inline" how the device is detected, pre-standard or af/at? and what class

also in the "minimum load" setup. compare this for both type of switches

maybe the  behavior is more predictable if you set power to static instead of auto?

but then it needs extra attention when the device is moved to another port

regards,

Pieter

[KalpeshDiyora1281]

Hi Sir,

Thanks for the support.

Please refer my reply as per below.

We have verified the detection and classification and it is working fine. Switch is releasing 53V after successfully completion of the detection and classification stage. Our POE module is getting initialize and we get voltage on output of the POE module. We also received Ethernet ping of our device initially.

Diode we have used is placed on output of the POE voltage. This is for the power oring of adapter and POE output.

It is not disturbing the detection and classification stage.

We also able to get few network ping of our device through Cisco switch.

But, Cisco switch drops power on POE line due to not maintaining the MPS(Maintain Power Signature). This switch drops ethernet link during the power drop. We observed device went off-line while Cisco switch drop power on POE line. Ping get missed at that time.

We guess, Cisco switch is disabling the data along with power drop.

Our device is connected with 13VDC secondary source and due to high voltage of adapter, device will consume power from adapter.

Power drop on Poe line is understood but Switch should not drop the data line.

We have one Cisco switch SG300 series with us and we have verified this scenario with that switch. It is working fine but 2960 series of Cisco switch is creating above-mentioned issue at customer place.

Please advise any configuration in switch to keep the data communication continuously "ON".

[pieterh]

I can see you have done some elaborate testing.

And i the end it comes down to different behavior of the two switch models.

       power inline {auto [max max-wattage] | never | static [max max-wattage]}

Did you try "power inline  static [max max-wattage]" variant ? and can this be an acceptable solution?

[KalpeshDiyora1281]

Sir,

Thanks in advance.

We have not tried "power inline  static [max max-wattage]"  and we don't know how to do it. Can you please suggest in detail. What will happen with applying this setting?

Is there any configuration in which switch drop Ethernet link if power get dropped due to not maintaining MPS?

Can we do change in 2960 switch configuration to keep the Ethernet link connected even if Power get dropped continuously due to MPS issue?

[pieterh · Accepted solution]

Can we do change in 2960 switch configuration to keep the Ethernet link connected even if Power get dropped continuously due to MPS issue?

-> as concluding from your own tests you can't!

the switch regards a drop of power consumption as a link-disconnect,

depending on the rest of the interface configuration the switch will restarts the negotiation of speed/duplex/ mdi-mdi-x, and maybe also spanning-tree detection

During this renegotiation, data transfer is paused for some time.

"we don't know how to do it" ??? I can't follow you here!

I assumed you know how to configure a switch and it's interfaces

login into the switch,  enter privileged mode ,  enter interface configuration mode en configure inline power setting

enable

configure terminal

 interface gi1/0/1

    power inline  static

   end

what will happen is The switch allocates power to a port configured in static mode before it allocates power to a port configured in auto mode.

I can't guarantee this will solve your issue, but nothing wrong to try it out

[KalpeshDiyora1281]

Sir,

We have tried this command in past but at that time it does't work..

For validation, We will try once again..

Before doing that, We would like to understand the below points.

1) Does port will disable the signature and detection period in this static mode? 

2) What will happen if non POE device will get connected on this static configured port? Will it damage that device due to this mode?

This issue is at Costumer end and we have limited trial to catch this issue. So, we would like to suggest the iteration before verifying the other aspects.

We have below Cisco model in our hand.

SG300-28PP.

We have simulated the issue at our end. This Switch is dropping the power due to not maintaining MPS. But, Ethernet link was not drooped. Device remain connected. We have verified the Ethernet ping.

Is this any issue with 2960/3750 switch setting? B'cos the issue observed with 2960 and 3750 series switch at customer end.

[pieterh]

you keep repeating the same question over-and over again.

you want to do something in an unofficial setup, which apparently do not work in all situations.

I cannot repeat your experiments and therefore cannot give the complete answer

I can only do some suggestions, but run out of ideas now, so this will be my last response to this thread

Good luck

Pieter

[KalpeshDiyora1281]

Dear Sir,

Have tried much with existing cisco switch to simulate at our end with SG300 Series but we not succeed to re-produce the issue at our end.

We could not understood if this two series 2960 and SG300 having the different configuration set up and behavior or not. 

Please suggest any other ways to trie and come out from this issue.

Thanks in advance for the co-operation and support.

[KalpeshDiyora1281]

HI,

Can you please suggest the alternate way to resolve this issue.?

[pieterh]

from the TI documentation
The TPS23753 supports a number of input-voltage ORing options including highest voltage, external adapter preference,
and PoE preference

"We have set adaptor priority by adjusting POE voltage less compare to Adaptor voltage."
-> switch to PoE preference