How to Disable SIP ALG on the DrayTek Vigor Legacy Models (firmware pre-3.8.5)

SIP ALG (Application Layer Gateway) is a feature which may be enabled by default on most DrayTek Vigor routers and inspects VoIP traffic as it passes through and modifies the messages on-the-fly.

In few situations this is useful, but in most situations SIP ALG can cause problems using the service. Very often, SIP ALG is poorly implemented causing VoIP messages to be modified in a harmful way or simply corrupts them. In such cases you may experience issues registering your handset, one-way or no audio, unable to receive calls, and issues with Busy Lamp Field (BLF) and Message Waiting Indicators (MWI).

For our Hosted VoIP service, including out Single User services, SIP ALG must be disabled on your DrayTek Vigor router.

This guide explains how to to disable SIP ALG on the following DrayTek models which are running firmware versions older than 3.8.5:

  • Vigor 2760
  • Vigor 2800
  • Vigor 2820
  • Vigor 2830
  • Vigor 2832
  • Vigor 2860
  • Vigor 2862
  • Vigor 2920
  • Vigor 2925
  • Vigor 2926
  • Vigor 2952
  • Vigor 2960

Even if your particular DrayTek model is not listed, these instructions should still apply if your model is in the same series.

If your DrayTek Vigor router is running firmware version 3.8.5 or newer then please refer to the following guide:

  1. Press the Windows Start button and in the search box type in cmd and hit Enter
  2. Type in
    telnet 192.168.1.1

    and hit Enter
    Note Recent versions of Microsoft Windows may not have Telnet installed by default.
    To install Telnet, click on Start → Control Panel → Programs → Programs and Features → Turn Windows Features on or off → Ensure TELNET CLIENT is checked and click OK.

  3. When prompted, enter your router username and password.
    The default username is admin and the default password is admin
  4. Type in
    sys sip_alg 0

    and hit Enter

  5. Type in
    sys commit

    and hit Enter to save the newly applied change

Further Reading

SIP ALG on DrayTek Routers at at www.draytek.co.uk (registration required to see article).

For information on setting up Quality of Service (QoS) see this guide.

If you are running firmware version 3.8.5 or newer then please refer to How to Disable SIP ALG on the DrayTek Vigor Series Routers (firmware 3.8.5 and newer)