Very High Proportion of CRC error with I connect Cisco Phone 7940 Series

[Enzoly]

Hello.

I have a problem of Very High proportion of CRC error when I connect a Cisco 7940 phone to my Meraki MS355-24, immediately the port is blocked.

I changed several patch cords, but it doesn't work properly. Does anyone have any idea about this error? how can i solve it?

Thank you

[alemabrahao]

CRC means Layer 1 issue. Have you tested It on another port or switch?

[Enzoly]

Hello Alemabrahao.

I plugged the same phone into another port, but I throttled the connection to 100 mb and I see this now:

UDLD had detected a TX/RX loop.

After that, it disconnects the port and sends me the message:

Very high proportion of CRC errors on port 12

[Enzoly]

Hello Alemabrahao.

I plugged the same phone into another port, but I throttled the connection to 100 mb and I see this now:

UDLD had detected a TX/RX loop

[ww]

Why is your port set to 100Mbit Fd?

Did you also set this manually  at the phone?  If not, try setting it back to auto

[Enzoly]

Hello.

Configure the port to 100 Mbit because if I leave it automatic it does not connect. In addition, the phone does not turn on even though PoE is enabled.

I have a meraki MR57 AP connected, and it works correctly, but I connect the phone and it doesn't want to turn on.

[Brash]

Cisco 7940's only support Cisco's proprietary PoE implementation, which is not available on Meraki switches. Therefore it's expected that the phone will not power up via PoE.

https://community.cisco.com/t5/ip-telephony-and-phones/7940-and-802-3af/td-p/795794

As for your other comment with CRC's and the phone only communicating when brought down to 100Mbps - that smells very much like a layer 1 problem somewhere along the line. Replace the cable (and SFP if applicable).

[Enzoly]

Hello Brash

But Cisco and Meraki are not the same, excuse my ignorance but supposedly it should be compatible if they are Cisco?

[Brash]

Meraki begun as a separate company and was acquired by Cisco. Therefore they don't typically use Cisco proprietary features, but opt for industry standards.

One example of this that comes to mind is Spanning Tree.

To be honest, I'm not even sure whether Cisco still uses their proprietary PoE implementation over the standard these days (haven't deployed a Cisco IP Phone in years).

[Enzoly]

What happens if I buy the power of the phones? should it work?

[Brash]

If the phone has an external power supply, it won't require PoE and therefore it will resolve your issue of the phone not powering up.

I'm not confident it will solve all of your CRC issues though.

[Enzoly · Accepted solution]

Thank you all for the comments and the time invested. Thanks.

[OVERKILL]

Nope, the 8xxx series phones just use standard PoE. 

[Enzoly]

After that, it disconnects the port and sends me the message:

[PhilipDAth]

The 7940 is very very very old.  I think @Brash is right.

I would look to a solution to replace the 7940s.  It's amazing they are still running!

[RaymondChance]

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@Enzoly wrote:

Hello.

I have a problem of Very High proportion of CRC error when I connect a Cisco 7940 phone to my Meraki MS355-24, immediately the port is blocked.

I changed several patch cords, but it doesn't work properly. Does anyone have any idea about this error? how can i solve it?

Thank you

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Common Causes and Solutions: CRC errors can be caused by a number of factors. Typically they are caused by either defective cable, transceiver (SFP), switch port, upstream network device, etc. To address this error, try replacing the cable or transceiver (SFP) and check the switch port and upstream network device.

source : IMDB Support