VoIP issues and three broadband

Mmaypoll — Sat, 31 Jan 2026 17:47:13 GMT

Set my mother in law up with three broadband and VOIP via vonage and all was working fine for making and receiving calls (when the internet connection was not down, but that’s another issue)
Just recently outbound calls stopped working while inbound calls still work fine. I get a dial tone and can hear the number tones but then nothing.
Long call with Vonage support where they did the usual reboot, reset, update firmware etc but no change. Yesterday they came back with a request to contact her broadband provider (three) and ask to change the below settings:
Enable DMZ
Disable SIPALG
Increase MTU size to maximum
Lower the firewall

There’s nothing on the EERO settings for any of the above so can someone please help me understand if/how I can do this on the three 5g hub please? The hub is the outdoor one, I think model name is Y5-210MU
Thanks in advance

Re: VoIP issues and three broadband

Anonymous — Sun, 01 Feb 2026 15:51:36 GMT

Hi, that is very odd behaviour. When I get VoIP problems it tends to be incoming calls stop working or nothing works and it's because Three have started to CG-NAT my connection.

Does your VoIP provider have a STUN server? and is that configured on the gateway device?

topic VoIP issues and three broadband in Broadband

VoIP issues and three broadband

Re: VoIP issues and three broadband