VoIP Not Working After Changing Router or Broadband Provider

Why VoIP Breaks After a Router or Broadband Change

You have just changed your router or switched broadband provider, and now your VoIP phones have stopped working. This is an extremely common scenario, and the good news is that it is almost always fixable with a few configuration changes on your new router.

The reason VoIP breaks after a router change is that your previous router had specific settings configured for VoIP — either by you, your IT team, or your VoIP provider. Your new router has different default settings that are not VoIP-friendly.

The Most Common Causes

1. SIP ALG Is Enabled on the New Router

This is the cause in the majority of cases. Most routers ship with SIP ALG (Application Layer Gateway) enabled by default. SIP ALG modifies VoIP packets as they pass through the router, breaking call setup, registration and audio. Your old router either had SIP ALG disabled or handled it differently.

See our detailed guide on what SIP ALG is and how to disable it.

2. Different Firewall Defaults

Your new router may have a more restrictive firewall that blocks SIP signalling (port 5060) or RTP audio (ports 10000–20000). Your old router may have had these ports explicitly opened or had a more permissive default firewall policy.

3. No QoS Configured

If your previous router had Quality of Service (QoS) rules prioritising voice traffic, your new router will not have these settings. Without QoS, voice traffic competes with all other data, potentially causing choppy audio or call quality problems.

4. Different NAT Behaviour

Different routers handle NAT (Network Address Translation) differently. Your VoIP phones may have been configured for the NAT behaviour of your old router. The new router may use a different NAT type (symmetric vs cone NAT), causing registration failures or one-way audio.

5. Changed Public IP Address

If you switched broadband provider, your public IP address has changed. If your SIP trunk uses IP-based authentication (where your provider whitelists your IP address), your new IP will not be authorised and all registrations will be rejected.

Complete Fix Checklist

Work through this checklist in order to get your VoIP working on your new router:

Step 1: Disable SIP ALG

Log into your new router's admin interface
Find the SIP ALG, SIP Passthrough or ALG settings (usually under Advanced, Firewall or NAT)
Disable SIP ALG completely
Save the settings

This single step resolves the issue in most cases. See our router-specific SIP ALG guide for instructions for BT, Sky, Virgin and other common routers.

Step 2: Open SIP and RTP Ports

Allow UDP/TCP port 5060 outbound (SIP signalling)
Allow TLS port 5061 outbound if your provider uses encrypted SIP
Allow UDP ports 10000–20000 inbound and outbound (RTP audio)
Allow UDP port 3478 outbound (STUN for NAT traversal)

See our firewall configuration guide for detailed instructions.

Step 3: Configure QoS

Set up QoS rules to prioritise traffic on UDP ports 5060 and 10000–20000
If your router supports DSCP-based QoS, prioritise packets marked as EF (DSCP 46)
Consider limiting bandwidth for non-critical applications during business hours

Step 4: Check NAT Settings

If your router offers NAT type options, use Full Cone NAT if available (most VoIP-friendly)
Avoid Symmetric NAT which is the most problematic for VoIP
Enable consistent NAT or NAT mapping preservation if your router offers these options

Step 5: Reboot Your Phones

After making router changes, reboot all VoIP phones. They need to establish fresh SIP registrations through the new router. Simply unplug each phone from power, wait 10 seconds, and plug it back in.

Step 6: Update Your IP Address with Your Provider

If you changed broadband provider and your SIP trunk uses IP-based authentication:

Find your new public IP address (visit whatismyip.com)
Log into your VoIP provider's admin portal
Update the authorised IP address to your new public IP
Wait a few minutes for the change to propagate, then reboot your phones

Step 7: Re-Provision Phones if Needed

If your phones were auto-provisioned by your provider, they may need to be re-provisioned to pick up any configuration changes. Check with your provider whether re-provisioning is required after a network change.

Tips for Specific UK ISP Routers

BT Smart Hub

Access at 192.168.1.254. Disable SIP ALG under Advanced Settings > Firewall. BT Smart Hubs have a relatively restrictive firewall — ensure SIP ports are not blocked.

Sky Router

Access at 192.168.0.1. Sky routers have limited VoIP configuration options. If you cannot disable SIP ALG, consider putting the Sky router into bridge mode and using your own VoIP-friendly router behind it.

Virgin Media Hub

Access at 192.168.0.1. Check for SIP ALG under Advanced > Firewall. If options are limited, switch to Modem Mode and use a dedicated router (such as a Draytek Vigor) that provides full VoIP configuration control.

TalkTalk Router

Access at 192.168.1.1. Check Advanced settings for SIP ALG. TalkTalk routers generally have basic configuration options — a third-party router may be needed for full VoIP control.

Still Not Working?

If you have worked through the entire checklist and VoIP is still not functioning, contact our support team. We can remotely diagnose the issue by analysing SIP registration attempts and call traces from our platform, and guide you through any remaining configuration changes.