Why is it a problem ?

SIP ALG generally affects incoming calls only. If you’re users are reporting ringing with no voice on answer you’ve probably encountered a SIP ALG issue on your router (for more information see disabling SIP ALG).

You’ll need to access the router to disable SIP ALG. If if whatever reason you access your router, consider switching your phone or PBX to TLS encryption (preventing SIP ALG) by changing the following two settings on your handset or IP-PBX.

  • proxy:
  • port: 5061
  • Transport: TLS

If you are unable to access the router consider switching your phone’s transport from UDP to TLS which will encrypt the SIP packet ultimately preventing the router from corrupting the SIP messages (see TLS). Highly recommended.

Disabling guide

While we periodically update this document the following articles are guides only and are offered as best efforts.

Cisco IOS Router

  • From the CLI: Enable configure terminal, No IP nat service SIP UDP port 5060
  • For TCP run: No ip nat service sip tcp port 5060

DrayTek Routers

This guide specifically applies to the Vigor 2760 but is also applicable to most other DrayTeks in the series.

  • 2800, 2820, 2830, 2860, 2920, 2925, 2960


  1. Start | Cmd
  2. Type: telnet (Enter) NB – Ensure Telnet is enabled ( Start | Control Panel | Programs | Programs and Features | Turn Windows Features on or off | TELNET CLIENT >> OK)
  3. Default user name: admin | admin
  4. Type: sys sip_alg 0 (Enter) Enter

Juniper JunOS Router

  • From the CLI: To verify if SIP ALG is enabled or disabled run show security ALG status | match sip
  • To disable run:
  1. Configure
  2. Set security alg sip disable
  3. Commit

Netgear Modem Router

This guide applies to most Netgear routers

  1. In browser browse to (this is the default IP address)The default username is admin and the default password is password
  2. Under Advanced select WAN Setup
  3. Check Disable SIP ALG option
  4. Select Apply


This KB applies to all SonicWALL SonicOS firewalls.

SonicWall has a feature called SIP Transformations that consistently cause total or partial loss of voice.

  1. Log into the web interface on the SonicWall.
  2. On the left, find the VOIP tab. Depending on the version of SonicOS your screen may appear slightly different.
  • Disable SIP Transformations: Browse to the SIP Settings page and ensure Enable SIP Transformations is NOT enabled.
  • Enable Consistent NAT: The Consistent NAT setting will ensure the same NAT port is used. If this is disabled, you may experience undesired call behaviour.
  • Ensure Consistent NAT is Enabled

This KB applies to most TP-LINK routers.

On Windows 7/8

  1. Start | cmd >>Enter
  2. Type:telnet – Ensure Telnet is enabled ( Start | Control Panel | Programs | Programs and Features | Turn Windows Features on or off | TELNET CLIENT >> OK)
  3. Default user name: admin | adminNote that no symbols may appear when typing in the password, but continue anyway.
  4. Type inip nat service sip sw offEnterIf successful, it should say Nat SIP v2 switch off!

Billion 7300GRA, 7800

Zyxel Equipment

Web UI: Using the Web Interface Navigate to the NAT tab and uncheck the box for SIP ALG.

Using Telnet

  1. Telnet into the router Select menu items 24 then 8
  2. To display current SIP ALG status run the following command:


While the following KB guide specifies the NB604N all Netcomm routers are similarly configured. Netcomm also provide a useful router emulator for all their routers (see emulator)

  1. Logon to the router
  2. Advanced Setup | NAT | ALG >> uncheck “Enable SIP”

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