Ubiquiti UDM-SE with Slingshot NF18-Mesh VOIP Issues

Forums › LAN (ethernet/Wifi/routers/Bluetooth) › Ubiquiti UDM-SE with Slingshot NF18-Mesh VOIP Issues

gokiwi64

39 posts

Geek
+1 received by user: 9

#324662 9-May-2026 15:25

Hi All, After some help, suggestions, advice.

I have a Ubiquiti UDM-SE directly connected to an ONT - The ISP is Slingshot. I have their NF18-Mesh connected to the UDM-SE so that the voip phone can work - and it has been absolutely fine for absolute months.

Then last Wednesday evening the phone went into a "Registration Status" = Down, "Hook Status" = On Hook.

I have rebooting the NF18 and even the UDM but to no avail - The Registration Status stays "Down".

From the vlan that the NF18 is in I can ping voice.slingshot.co.nz and all ports are open on the UDM's firewall.

Am at a bit of a loss as to what else I can do and why it would suddenly change.

So any (constructive) help greatly appreciated.

Regards

bj99

171 posts

Master Geek
+1 received by user: 24

#3489207 9-May-2026 16:07

Try disabling SIP ALG on the UDM.

JemS

92 posts

Master Geek
+1 received by user: 46

ID Verified

#3489208 9-May-2026 16:16

bj99:

Try disabling SIP ALG on the UDM.

On the UDM this will be under the firewall tracking options under the console settings in the device manager.

Also try setting an exemption for the ip of the slingshot router in the ips/ids settings.

Join Mercury and I’ll get bonus rewards points. Make sure you use my referral link to explore their wonderful offers. https://www.mercury.co.nz/join?m_copc=FGF50&m_rc=100211888685

Router: UXG-Lite

AP's: 2x U6-Pro, 1x U6-Lite, 1x UK-Ultra, 1x AC Mesh Pro

Phone: S26 Ultra

Wearable: Garmin Forerunner 955

gokiwi64

39 posts

Geek
+1 received by user: 9

#3489227 9-May-2026 19:33

I hve checked SIP - It was wasnt checked , so that should be all good. But I have created an exception, so will sww how that goes .

Thanks :-)

yitz

2251 posts

Uber Geek
+1 received by user: 604

#3489228 9-May-2026 19:42

Have you checked the SIP is connecting on the correct interface i.e. WAN or bridged/LAN and that the WAN interface is untagged Ethernet WAN etc.

Surely the Netcomm has logs you can check also?

With Slingshot, you can request ONT voice also if that would work better for you.

JemS

92 posts

Master Geek
+1 received by user: 46

ID Verified

#3489229 9-May-2026 19:50

gokiwi64:

I hve checked SIP - It was wasnt checked , so that should be all good. But I have created an exception, so will sww how that goes .

Thanks :-)

My exception took quite a few hours to take effect. Then my sip phone started working again.

Join Mercury and I’ll get bonus rewards points. Make sure you use my referral link to explore their wonderful offers. https://www.mercury.co.nz/join?m_copc=FGF50&m_rc=100211888685

Router: UXG-Lite

AP's: 2x U6-Pro, 1x U6-Lite, 1x UK-Ultra, 1x AC Mesh Pro

Phone: S26 Ultra

Wearable: Garmin Forerunner 955

gokiwi64

39 posts

Geek
+1 received by user: 9

#3489292 9-May-2026 21:13

I guess I will have to wait overnight then, it was registered for about 2 hours then reverted to down again.

If not it looks like I will have to disconnect the UDM and put the NF18 back as a direct connect to the ONT - There could be a heap of Ubiquiti gear going on the market soon - all because of a damned analogue phone that only 2 people call.

Technology is great until its not.

Geekzone support

Support Geekzone with one-off or recurring donations Donate via PressPatron.

shk292

2919 posts

Uber Geek
+1 received by user: 2040

Lifetime subscriber

#3489309 10-May-2026 10:23

Do you need an actual analogue phone connected or could you transfer the number to a voip provider and use an app to answer incoming calls?