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New Member

cat 3850 and PoE

I'm a little befuddled on this, but I might be missing something. We are deploying a 3850 stack, with avaya IP phones. What I am seeing looks like a SW bug.

The avaya CM is not in place, so the phones can't register and they go into a reboot loop. The 3850 looks like it is calculating the allocated poe additive, and even though there are ~20 phones connected to the 1st switch in the stack, I am getting "power denied, insufficient poe". The phones draw 4w, and total power for mod 1 is 1440 W. But everytime the phone reboots, it looks like the switch is adding to the power allocated and eventually runs out of poe.

If I shut down the ports, nothing changes as far as allocated or available power. If I issue power inline never, nothing changes as far as allocated or available power. This doesn't seem to be the right behavior, I thought the switch should reclaim the power since it is not in use. At this particular point in time, with all ports configured with power inline never, I see:

Module   Available     Used     Remaining

          (Watts)     (Watts)    (Watts)

------   ---------   --------   ---------

1          1440.0       38.0      1402.0

I am positive that once the avaya CM is in place and the phones can register with it (thus stop rebooting constantly), this symptom would go away. But the issue would still remain, I think, unless the lldp-med advert from the registered phone would cause the used/remaining power totals to be recalculated. I'll know more for sure on Thursday once the CM is installed. But this behavior seems a bit odd to me (once again, unless I am not understanding something). Has anyone seen this type of behavior, or does anyone have any explanation? Thanks, chris

8 REPLIES
Cisco Employee

cat 3850 and PoE

Hi Chris, What code version are you running on the 3850? 3.2.1 or 3.2.2?

New Member

cat 3850 and PoE

Richard,

it's 3.2.2. I did verify that this also was the version they shipped with, and these have not been upgraded.

thanks,

chris

Re:cat 3850 and PoE

Cisco switches need CDPto allocate power. Avaya phones do not use cdp hence yu will get this behavior.

I would suggest yu manually allocate power per interface....


Switch(config-if)# power inline {auto [max milli-watts] | never | static [max milli-watts]}


Hope this helps...


Sent from Cisco Technical Support Android App

New Member

cat 3850 and PoE

Mandlenkosi,

I realize that the switch will allocate based on cdp adverts.

We are using avaya phones in numerous places across multiple platforms, with lldp enabled. We do not see any switches running out of available poe anywhere else but on this 3850. The switches see the lldp advert, know that the phones are a class 1 poe device, and allocate the 4 watts with no problems. Even if there was not any type of advert, my understanding is that max power would be allocated based on the class of device, so we still would not be running out of poe.

The second problem is that the switch seems to be allocating in an additive manner. The phone comes online, gets 4w allocated, reboots, gets another 4w, reboots, gets another 4w. So if I leave only one phone online the switch would eventually run out because it keeps adding to the total. This does not seem right to me. In other words, if 1 phone is powered, and it reboots 6 times, the switch will show 28w used, not 4w used.

At any rate, I'll know more this afternoon, as the phone group will be installing the avaya CM today. My suspicion is that once the phones can register and load their profile this won't be a problem. Even if this isn't the case, the phones won't be in a constant reboot and the switch should still be ok, even if the total power used doesn't show what is actually used.

chris

Cisco Employee

cat 3850 and PoE

Chris,

we do have a few outstanding POE bugs in 3.2.2 however those symptoms don't ring a bell.  I would highly recommend opening a tac case for further investigation.

lp

"my understanding is that max power would be allocated based on the class of device, so we still would not be running out of poe."

-This is correct

New Member

cat 3850 and PoE

Richard,

I'll be opening a case today. We've gone from one extreme to the other on this. The avaya comms mgr was installed yesterday, so the phone provisioning went well. But now instead of running out of poe, the switch is saying we're not using any (with 41 phones and 10 APs):

Module   Available     Used     Remaining

          (Watts)     (Watts)    (Watts)

------   ---------   --------   ---------

1          1440.0        0.3      1439.7

2          1440.0        0.0      1440.0

3          1440.0        0.3      1439.7

something definitely appears out of sorts with this. switch 3 in the stack especially should be showing 154w used since that's where the APs are plugged in (they are the 3600 series).

chris

Cisco Employee

cat 3850 and PoE

Hi Chris

As reference, in the case that someone else sees this issue - the bug is CSCuj64918

cat 3850 and PoE

Try setting LLDP enable .

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