ARP broadcast being blocked?


I am having issues with some of my Cambium PMP450 APs which seem to be blocking the ARP requests, therefore generating connection problems between sites.

The topolgy is:

ClientA – SM1 – AP1 – Switch – AP2 – SM2 – ClientB

If I try to ping from ClientA to ClientB, ARP request (broadcast) leaves ClientA but it never reaches ClientB (I can confirm this using Wireshark). If I ping from ClientB to ClientA (so the ARP requests starts from the other end) ping starts working.

Everytime ClientA needs to populate its ARP table with ClientB adresses, the problem starts again.

SMs firmware version is CANOPY 20.0.1 SM
APs firmware version is CANOPY 20.0.1 AP


  • Protocol filtering is disabled on the SMs and APs.
  • When I reboot ClientA SM, it seems to randomly start working (for a few seconds).
  • I have checked both APs configuration and it seems like they are exactly the same.
  • I have found that this is happening in 2 of the APs that we have on that site.
  • If I configure a SVI on the switch (Huawei), on the VLAN and subnet that SMs use for Management (they do not use to communicate with each other on daily operation, so ARP entries do not exists on the their tables) it doesn’t work either.

Thank you in advance for any help you can provide.


This sounds like a common route table issue. Most likely within your tower switch but that is not alway 100%. The indicator is that ping fails one way but both ways work after the otherside has pinged first. This enters a route in the bridge table of each AP and the switch forming the path which will stay active as long as there is traffic from one SM to the other. If you stop the traffic for a while, about 5 mins, then your back to square one.

Double check that the SMs are in bridged mode and have basically identical network setup as in your case SM “b”, the APs have identical network setup and the switch ports are trunk ports with no protocol blocking enabled or ACLs applied.
If you are using vlans and this is a spanned link through your network, ensure the switch has the vlan in its table and active without ip assigned to the vlan.
If you need the SMs in router mode, ensure you add the correct subnets to each SM with a route to the other SM. The wireless side acts as a wan port in this mode.


This sounds like a known issue with 20.0.1 firmware. It was fixed in version 20.1 and listed in the release notes:
Problems Corrected
Products affected: 450/450i/MicroPoP AP
Tracking: CPY-17055
Description: Addressed customer issues with Broadcast channel stopping transmission
and loss of communication to SMs until AP was rebooted.

I recommend upgrading to

Sorry for the inconvenience,


Hello Douglas, thank you for your reply.
This does not seem to be the case, every configuration on the switch ports for the APs are exactly the same, no acl has been placed.

Thank you.

Hello Charlie, thank you for your reply.

I wasn’t aware of this problem in v20.0.1, we are going to upgrade these APs and run the tests again.

Thank you.

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Hello Charlie,

We update AP to and the issues seems to be solved.

Thank you very much for your help.

Best regards,


You’re welcome! Thanks for following up.