BLF Requirements - strange problem


I currently have about 30 Sangoma S500 phones spread over 2 different offices. All of the phones connect back to an off site FreePBX server.

Freepbx server has latest modules and system updates installed. (Using the distro)

Firmware is up to date on the S500s.

The issue I have is at one of the location the BLF lights are not working. I have tested using the same extension at the other location and the BLF lights work. So it must be something related to the network at the problem location.

Both networks are set up just about the same.

To help me troubleshoot does anyone know what/if there are any network requirements for BLF to work?


Any idea how I would start to troubleshoot this?

There’s obviously a difference in the network setup.
Can you tell us how your network is setup?
VPN? Is this issue only for extension BLF monitoring or also for feature codes?

Both offices have a Cisco router with a zone based firewall. Both firewalls are setup with the same rules, etc.

The problem office has a slightly router that uses Cisco IOS XE instead of “normal” IOS.

No VPNs, just straight out to the Internet with NAT. PBX server is cloud based.

The issue is with BLF for extensions.

Could you advise how I would test the feature codes to rule this out?

Make a BLF key with the value = *21EXT this will monitor FMFM, it should turn red when FMFM is enabled, Green when disabled.
(Replace EXT with that phones extension number)

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