Cisco 2960 and Avaya phones - ports on switch go down/down

[Andrew Reid]

                   We have a very interesting problem. Our customer has a 3750 core switch with DHCP for both voice and data. There are also 2960's linking back to the core on trunks. The user base mostly have PC's/MAC/s plugged into the Avaya phones.

There are about 90 people connected into the 2960 24 port switches.

When the customer starts someone new and connects them into one of the 2960 switches someone on any one of the switches gets put off the network. If we look at the port on the switch that this person is on, the lights are off, and if I connect to the switch and look at that port its down/down. If we then go and repatch this PC to another port it comes back up again. This happens everytime a new PC is connected to the network. If 2 PC's are connected, 2 other PC's get put off the network until they are connected into another switch port. There are no common ports or switches. in fact we did a test  - A pc that was put off the network was moved to a different port and connected back onto the network. We then moved them back to their original port and it continued to work there. The customer has to do whis for every new connection to the network.

They have wireless users also on this network using the same subnet and same dhcp scope on the 3750, there are no issues here with new PC's connecting

We have had a look at the POE power being used by the phones on each of the switches, and they are only using about one third of the avaliable power. 

Nothing in the logs

Has anyone seen anything like this before??

[Leo Laohoo]

There are about 90 people connected into the 2960 24 port switches.

How did you manage to squeeze 90 people into a 24-port switch?

Can you post the interface configuration?

[Andrew Reid]

I did say the 2960 switches ( not switch), there are 4 2960's and one 3750. I'll try and get a config up on Monday morning. I'm just about to go home here.

Thanks

[Leo Laohoo]

Sounds like a cabling issue to me.

[dfrosty1974]

Andrew,

Yes I have seen this. I'm a engineer for Avaya and have seen on the 2960 - 48 port unit. It with it starts shutting down ports after about 40+ ports are connected. I think there are a few different wattage power supply versions for the 2960 POE switches. And if I remember the customer I had had a smaller power unit.  As for the 24 port unit, I would think this would only happen at 20+ ports are in use.

The real problem comes as how Avaya interpreted the IEEE 802.3af PoE standard and how Cisco did.  The Avaya phone on start up request a main POE class and state the can also do a higher class (due to adding a button module to the phone).  Cisco only take that the phone is going to be the higher class and reserves that amount of POE on the switch. So the amount of POE power in use if different then the reserved power you see.  Sorry I do not know if there is command in Cisco IOS to see the "reserved POE power" vs. the “in use POE power”.

There is no workaround as Cisco states they are using the IEEE 802.3af PoE standard correct and Avaya states they have used the standard correct in the phones FW.

I did found this FAQ that talk about the 370w power supply of the 3750 (same specs of the 2960).  A Catalyst 3560 switch with 48 ports supports 370W. Because C7941G-GE is a Class 3 device, it requires up to 15.4W. Can this be reduced to 7W so that the switch can power all 48 phones?

http://www.cisco.com/en/US/products/hw/phones/ps379/products_qanda_item09186a00808996f3.shtml

- Frosty

[Andrew Reid]

I did consider the power side. When I looked at what was used and what power was available the switches would only be using a third or half of what could be supplied with the balance showing up as available.

When i went to the customer site to do a test, we did not even connect through a phone and still someone got put off the network.

Did you do anything to resolve, or just not use all of the ports.

Andy

[Leo Laohoo]

It with it starts shutting down ports after about 40+ ports are connected. I think there are a few different wattage power supply versions for the 2960 POE switches.

Hi David,

I believe this is incorrect.  The 48-port 2960 PoE (and there's only one model) is the WS-C2960-48PST and it has 370w of PoE shared to 48 ports.  If each port uses up to 7.0w then the switch will happily supply power to all 48-ports (have you heard a 48-port 2960 supply power to all 48-ports?  It's scary!). 

[dfrosty1974 · Accepted solution]

I believe this is incorrect.  The 48-port 2960 PoE (and there's only one model) is the WS-C2960-48PST and it has 370w of PoE shared to 48 ports.  If each port uses up to 7.0w then the switch will happily supply power to all 48-ports (have you heard a 48-port 2960 supply power to all 48-ports?  It's scary!).  

Leolaohoo,

I stand corrected.  It looks that the 2960 in 24 ports POE only  has a 370W power supply.  It must have been a different model my  customer had that could hold a 2nd power supply. As the solution was to  add a 2nd power supply to be able to use all 48 ports on the switch in  POE mode.

Andy,

As for your issue.  What model Avaya phones are you using?  The  9600’s (like 9620/9630 phone) are class 2 IEEE 802.3af and will reserve  and max at 7.0 watts POE. There are some larger phones like the 9650  color and 1692 IP conference phone that are POE class 3 and will use up  to 15.4 watts. The new 96x1 (like 9641 and 9621) are class 1 and only  use 4.0 watts, but have a High/Low switch on the bottom to force them to  class 2 (7.0 watts) when needed.

What we found in the 48 port Catalyst till we added a 2^nd power supply was.

•        If you are running a older ISO it will not support the 802.3af standard  (only supports CDL) and so it place ALL ports into POE class 0  (default) maxing at 15.4 like a class 3.  – So a 370 watt power supply  can only support 20 ports at 15.4 watts.
• A work around is to  disable the POE on a few of the port (4-6) ports so not POE is reserved  for them. This will give POE to the other ports and then use the last  4-6 ports for PC or printers only.
• Also verify the Avaya IP phones have the most current FW.  Avaya changed the FW to work better with Cisco's interpretationof the 802.3af standard.  Not saying Cisco is using the 802.3af standard wrong, just different then Avaya did.

-Frosty

[Leo Laohoo · Accepted solution]

I stand corrected.  It looks that the 2960 in 24 ports POE only  has a 370W power supply.  It must have been a different model my  customer had that could hold a 2nd power supply. As the solution was to  add a 2nd power supply to be able to use all 48 ports on the switch in  POE mode.

The 3560E/X and the 3750E/X can support a second power supply.

To Andy,

Look at the product name of the switch of your choice.  In regards to PoE capable switch, "P" means PoE support.  HOWEVER, if you have an "F" in the suffix, it means FULL POWER and will be able to support (at least) 48-ports at 15.4w or 37-ports at  20.0w.

Of the 2960-range, there are only TWO models capable of doing so.  They are:

1.  WS-C2960S-48FPD - Supports up to 20.0w (PoE+) to 37 ports and 48-ports at full 15.4w.  1/10Gbps SFP/SFP+ uplink

2.  WS-C2960S-48FPS - Supports up to 20.0w (PoE+) to 37 ports and 48-ports at full 15.4w.  1Gbps SFP uplink

[Andrew Reid]

Thanks for the replies, I think indeed this must be something to do with Avaya/POE connecting to the Cisco switch.

http://www.watersystems4u.co.uk

Andy