High Data traffic loss with Dell N3248PXE-ON switch

Hi,

I would check the steps like this. First, try connecting another device that supports 2.5Gbps to the same switch port. If that doesn't work, connect the AP to a different 2.5Gbps port on the switch or even a different compatible switch if you have one. This helps you figure out if the issue is with the switch port, the AP, or something else. Next, check MTU. If the MTU is different between the AP and the switch, it could lead to packet loss, so make sure both are using a consistent MTU, usually 1500 bytes. Also, verify the VLAN configuration. If the AP and switch are on different VLANs without proper routing, they won't be able to communicate. Don't forget to check the Spanning Tree Protocol (STP) configuration on the switch port, as a misconfiguration could potentially block the port. Ensure the switch has enough power available for the AP, especially if you're using 802.3at, and try a different PoE port on the switch if possible. Make sure both devices have compatible firmware, and explicitly set the speed and duplex on the switch port, as sometimes auto-negotiation doesn't work as expected.

Hope that helps!

Hi @DELL-Erman O​ ,

As you mentioned, the MTU size is 1500 on both devices.

1. If we remove the AP and connect to other ports, it works (sometimes only), but on the same switch port, if we connect any devices, it won't work.

2. If we change the speed to 1G on the switch, the data traffic works between the AP and switch without any loss, but even if we set the speed to auto/2.5G on the switch port, it is not working out

3. Als,o we tried to set the power mode to AT manually on the switch port, which is also not working out (we referred to this case: https://www.dell.com/support/kbdoc/en-in/000209264/n2224px-n2248px-n3248px-port-flapping-continuously-when-connecting-poe-802-3at-device

4. We tried with no VLAN and with VLAN configurations, which did not solve the problem.

So do we have any command on the switch to see whether proper PoE power is delivered to a switch port and also properly distributed to other ports?

Thanks,

Vignesh. V

Hello,

The command to see consumed power at the switch is “show power inline". The above-mentioned article also recommends to disable green-mode which we commonly do to resolve such issues.

configure

interface gi 1/0/X

no green-mode eee

no green-mode energy-detect

end

Also, you say you have connected other device on that port and it still fails, but the same device works on another port. If the configuration on these 2 ports is the same, and the same device works on one port, but not on the other, then it can be a hardware issue with the switch port for which you can open a ticket with Dell support. You can test with a laptop in order to determine if the issue has anything to do with PoE or is it just packets not going through, which you can confirm by pinging from the laptop.

Hi @DELL-Charles R​ ,

With AP powered up using PoE injector and the data cable (with 2.5G speed )alone connected to the Dell switch (issue port), we still could see the high traffic loss issue. The issue is happening on some ports of the switch while other ports work fine. Any changes or settings need to be done for 2.5G on the switch or connected devices ( AP)?

Thanks,

Vignesh. V

Hello,

The Dell N3248PXE-ON switch the default detection mode for all interfaces is set to 802.3bt (60W).

As you can see in the spec sheet, 802.3bt is listed.

dell-networking-n3200-powerswitch-specsheet.pdf

https://www.delltechnologies.com/asset/en-us/products/networking/technical-support/dell-networking-n3200-powerswitch-specsheet.pdf

N3248PXE-ON IO/PS Airflow, with OS6: 48x RJ45 10M/100M/1G/2.5G/5G/10G 802.3bt (up to 90W) PoE auto-sensing ports; 4x 25G SFP28 ports, 2X 100G QSFP28 ports, 1x 1600W AC PSU included

You want to use 802.3at PoE (30W) which is not what the switch is made for. This document lists commands (as you pointed out) to set to mode 802.3at, however the commands are listed for N2224PX, N2248PX, and N3248PX, which is not your case.

Dell Networking PowerSwitch N2224PX, N2248PX, and N3248PX interfaces flapping continuously when connecting POE 802.3AT device
https://www.dell.com/support/kbdoc/en-in/000209264/n2224px-n2248px-n3248px-port-flapping-continuously-when-connecting-poe-802-3at-device

You can try to disable autonegotiation on the switch port and also on the AP port. And then hardcode the speed to 2.5 Gbps using “speed 2500”.

For this switch N3248PXE-ON, we do not have any other settings that you can check on, and you may need to see about using an AP that supports 802.3bt. 

Hi @DELL-Charles R,

* As mentioned earlier, we followed https://www.dell.com/support/kbdoc/en-in/000209264/n2224px-n2248px-n3248px-port-flapping-continuously-when-connecting-poe-802-3at-device this link to set the PoE power to AT mode on the switch, but still, we could see the issue

* We tried to disable the autonegotiation on the switch and AP, but still, when speed is set to 2500 on the AP and switch, we could see the issue​

* In most of the ports, we could see that the speed is negotiated properly to 2500 and no data loss, but in some ports we see this issue

* Even when we powered AP via PoE injector and connected only data line to AP from switch, still we see high data loss when speed is autonegotiated/manually set as 2500 on both devices.

* In all the above cases, if speed is set as 1000 in AP and switch, we don't see the issue

Do we have any stats counter in the Dell switch to find the reason for this issue?

Thanks,

Vignesh. V

Hi @DELL-Charles R , any update on the above post ?

Hi, I think you can use "show interfaces counters errors"

And on S series these command gives some information regarding ports for example "show queuing statistics interface ethernet 1/1/1" and "show queuing weights interface ethernet 1/1/1"

Hi,

We have replaced the switch with another Dell switch (model: N3248PXE-ON), but we still can see the issue on certain ports. We are using the same configuration as suggested in https://www.dell.com/support/kbdoc/en-in/000209264/n2224px-n2248px-n3248px-port-flapping-continuously-when-connecting-poe-802-3at-device . Any other possible suspects from the switch side?

Thanks,

Vignesh. V

Hi,

Just a heads up make sure you're running the latest firmware on the switch. Dell has fixed a bunch of PoE and 2.5G-related bugs in recent updates. The current version is 6.8.1.7, so definitely worth checking if you're up to date.

To see if the AP is getting enough power and negotiating properly

• Update firmware to version 6.8.1.7 to fix known PoE and 2.5G issues.
• Use show power inline to check PoE status and power draw per port.
• Manually set port speed to 2.5G full duplex if auto-negotiation fails.
• Disable EEE if compatibility issues arise.
• Use at least Cat 5e preferably Cat 6 cabling for stable 2.5G performance.