Consecutive POE ports fail - MikroTik AP not working

Publication Date:  2017-05-31 Views:  728 Downloads:  0
Issue Description

When multiple MikroTik AP software version 6.38.1 are connected on consecutive POE ports the PD's are not working - no power - the switch fail to provide power over ethernet.

The issue appeared on S5720-52X-PWR-SI-AC software version V200R008C00SPC500 when to the switch are connected more than one AP on consecutive ports – only one AP works without any problems.

 

Handling Process

1.  The first AP was powered on normally after it was connected to GigabitEthernet 2/0/29. The following figure shows the power information on this port:

2. After the second AP was connected to GigabitEthernet 2/0/30, the port turned to Up state but the PoE power on the port was 0. Only GigabitEthernet 2/0/29 port’s power increased.

The PoE state information obtained on the switch showed that only GigabitEthernet 2/0/29 was powered on, and GigabitEthernet 2/0/30 was still in power-off state.

3. After the third AP was connected to GigabitEthernet 2/0/31, the port turned to Up state but the PoE power on the port was 0. Only GigabitEthernet 2/0/29 port’s power increased. PoE state information showed that only GigabitEthernet 2/0/29 was powered on.

4. After the fourth AP was connected to GigabitEthernet 2/0/32, ports 29, 30, 31 all turned to Down state.

5. According to IEEE 802.3at/802.3af, PSEs support power supply over wire pairs 1/2 and 3/6, wire pairs 4/5 and 7/8, or both. PDs must be able to receive power from either wire pairs 1/2 and 3/6 or wire pairs 4/5 and 7/8, but they cannot transmit output power over these wire pairs. Huawei switches transmit PoE power over wire pairs 1/2 and 3/6.

 

 

6. We successfully reproduced the problem in our lab. After APs were connected to contiguous ports, only the port with the first connected AP had increasing power consumption and was powered on. Ports with APs connected subsequently were not powered on, and their power consumption was 0. Testing proved that the MikroTik APs transmitted output voltage through wire pair 4/5, which violates IEEE 802.3at/802.3af.

7. Four contiguous port share circuits in the switch. Non-standard APs connected to these ports transmit voltage over wire pair 4/5, causing the following problem:
8. All the four ports receive power from the port with the first connected AP. When the power consumption on the first port exceeds the rated power, all the ports are powered off and restart.

 

 

 

 

 

 



 

Root Cause

After APs were connected to contiguous ports, only the port with the first connected AP had increasing power consumption and was powered on. Ports with APs connected subsequently were not powered on, and their power consumption was 0. Testing proved that the MikroTik APs transmitted output voltage through wire pair 4/5, which violates IEEE 802.3at/802.3af.

Four contiguous port share circuits in the switch. Non-standard APs connected to these ports transmit voltage over wire pair 4/5, causing the following problem:


All the four ports receive power from the port with the first connected AP. When the power consumption on the first port exceeds the rated power, all the ports are powered off and restart.

Solution

Replace Non-standard APs

Suggestions

If you have only 2 or 3 non-standard AP's that need to be connected to the switch you can connect them on ports 1, 5, 9, 13...etc and it will work  - this could be a workaround.

END