Disable SIP ALG
An ALG is an 'Application Layer Gateway'. Typically it's software in a router that inspects VoIP traffic and modifies the information inside in order to try and help make VoIP work better. In practice they tend to make things worse. you may end up with one way audio, no audio or be unable to register.
Disabling an ALG on your router may well help with any VoIP problems. Here are some notes on various routers that we've come across:
ZyXEL VMG1312 and VMG3925
Usually disabled by default.
- Log in to the router's web interface
- Go to:
- Network Setting - NAT - ALG
- Disable the settings there
To completely disable the SIP ALG, you will need to connect via Telnet to your router.
:connection unbind application=SIP port=5060 :saveall :exit
(On older models/firmware the command to use is :nat unbind... rather than :connection unbind...)
- Click on ADVANCED, then CONFIGURATION
- Click on VIRTUAL SERVER
- Click on ALG
- Select DISABLE
- click on APPLY, then click on SAVE CONFIG
From Wan Setup Menu: go to NAT Filtering and check the box next to "Disable SIP ALG"
telnet in and:
kmodule_ctl nf_nat_sip disable kmodule_ctl nf_conntrack_sip disable
In the web interface, under Network > NAT, click the ALG tab then set the SIP ALG off
telnet in to the router and:
ip nat service sip sw off
If SIP ALG is disabled successfully, it will show Nat Sip v2 switch off! This will reset when rebooted and will need to be set again.
BT Business Hub
- Open a browser go to 192.168.1.254
- Click on ‘Advanced Settings’
- Enter your admin password the default admin password can be found on the bottom of the router).
- Click Continue to 'Advanced Settings'
- Click Firewall then 'Configuration' and scroll down to 'Application Layer Gateway'
- Click Yes next to 'Disable SIP ALG' and click Apply
ZyXEL 660 range
- telnet router
- Menu option "24. System Maintenance".
- Menu option "8. Command Interpreter Mode".
- Type in:
ip nat service sip active 0
- More info on: VoIP-Info