Not all SG300 ports supplying Inline Power (legacy / pre-standard PoE)

[aherrera]

Hello out there,

I have a strange problem occurring in our office. Essentially, not all ports on our brand new SG300-28P switches provide Inline Power to our older 7900 series phones. I can connect the phone a couple ports down and it usually powers up, but not always. Often I can also connect an 802.3af device to one of the troublesome ports and it will received power, however I am noticing there are some ports that now refuse to supply PoE at all

This is equipment that has been running perfectly fine for several years now, on C3524 PWR XL switches. I can also tell you that this is not isolated to one switch, but all 5 of our SG300 access switches. And, yes, the firmware has been updated to 1.1.2.0.

All thoughts and ideas are welcomed!

Thanks in advance,

Albert

[aherrera]

I've never heard of what I'm about to suggest, but could it be possible some device(s) is interferring with the PoE negotiation process? Although that does not explain why it only happens to certain phones. I would think all would be affected. It's a thought, though.

By the way, this idea occurred to me, after witnessing the link/act LED's blink nonstop across all ports on all switches (not the case when isolated).

Hopefully, tomorrow I have some time to load Wireshark on a laptop and see if that sheds any light.

Thanks again,

Albert

[David Hornstein]

Hi Albert,

It would also be interesting to look at the screen catpure of two pages

1. GUI options - Port management >POE>properties

2. GUI options - Port management >POE>settings

I am wondering if you are hitting a POE budget limit.

Also release notes indicate the following, which may be relevant since you are coming off an older switch.;

Problem:

The Cisco phone model 7960 (a legacy powered device) cannot power-up when using a cross-over cable.

Solution:

Use straight cable instead.

I am also guessing that since you are running a IP phone system multicast packets are causing the activity LEDs to flash in unison.  But I am not sure what you mean by "... blink nonstop across all ports on all switches (not the case when isolated)." 

What do you mean by not the case when isolated ?

regards Dave

[aherrera]

Hey Dave,

That is a very good idea, concerning checking the PoE budget, but all switches are utilizing under 20% of the 180W budget.

Also straight patch cables are only being utilized in our environment; have swapped out for new ones as well, to no avail.

Last but not least, we are running Call Manager v7.1.5... and you are correct, all activity LED's flash in unision. This is something that I had not witnessed whilst on the old C3524 switches. Additionally, when I disconnect the uplink to our distribution switch (C3750), the rapid flashing seizes.

[David Hornstein]

Hi Albert,

No, the screen captures are great, they show me that the POE budget is not part of the issue.

The switch error log  or even hyperteminaled into the console port (in CLI mode) may tell you what is happening when you plug a phone onto the switch.

A wireshark capture would tell us if multicast packets are causing the activity LEDs to flash in unison.  But i don't think that's the issue, maybe just a distractor.

Either check out the console messages when in CLI mode  and error log, they may be informative.

If you wish have a chat with the good folk at the Small Business Support Center (SBSC) at ;

http://www.cisco.com/en/US/support/tsd_cisco_small_business_support_center_contacts.html

regards Dave

[aherrera]

Thanks for the responses, David.

After going back and forth with SBSC for a week and a half, I was finally informed of the following:

Issue:

PD devices when sharing the same line transformer with Cisco IP phones 7960 with PID= 68-0808-xx may not power-up correctly at times. The occurrence of the problem depends on the sequence in which the PD devices and the IP phones are connected to the set of 4 ports served by a line transformer.

PD will not power-up when it is plugged-in to one of the ports in a 4-port set where a 7960 phone with PID=68-0808-xx  is already connected.  This should not happen if the PD is connected and powered-up before above phone is connected. (The phones have been EOL since 2001/2002.)

Workaround:

a.    When issue occurs, unplug the 7960 phone with PID=68-0808-xx and wait till the impacted PDs are powered up, then plug in back the phone. 

b.    Use Cat3 cable when connecting Cisco 7960 with PID=68-0808-xx to the switch.