VoIP telephony issues are often caused when the SIP Application Layer Gateway (SIP ALG) is enabled on a network router.

Preparation:

1. Identify your router’s IP address:

   • For Windows operating systems (all versions):

     • Open the Command Prompt (Start → Run, type “cmd” and press Enter).

     • Copy and paste the following command: ipconfig /all | findstr Gate (without quotation marks) and press Enter. Pay attention to uppercase and lowercase characters. If you have difficulty pasting, the | character can be entered using the keyboard by pressing Shift +.

     • One or more lines of text will appear in the Command Prompt. In one of them, you will find the text “Default Gateway” followed by a numerical value (usually in the format 192.168.XXX.XXX). This is your router’s IP address. Make a note of it.

2. Know your login credentials:

   • Make sure you know your router’s username and password.

3. Access the router:

   • Open a browser (e.g. Mozilla Firefox) and type the IP address retrieved in Step 1 into the address bar.

   • A webpage or login window will appear asking you to enter a username and password. Common usernames are "user", "admin", "Administrator" or "root". You can usually find this information in the quick start guide provided by your internet provider along with the router. Alternatively, you can find the manual online on your provider’s support page. If you still cannot find it, contact your provider’s customer support department. On some routers, the username/password combination may be printed on a sticker located underneath the device. modulus does not have access to this information. If you purchased the router separately, the credentials should be listed in the user manual unless they have been changed by you.

4. Log in to the management interface:

   • If you enter the correct username and password, you will gain access to the router’s management page. If the login window appears again or you receive the “Access Denied” message, the credentials entered are incorrect. Check uppercase/lowercase characters as well as similar-looking characters (e.g. I and l, S and 5, ni and m). Make a note of these details.

Speedport Entry 2i:

To disable SIP ALG on Cosmote’s most commonly used router, follow the process shown in the image below.

After logging into the router using its IP address, follow these steps:

1. Select the Internet tab.

2. Open the Security submenu.

3. From the tab list, select ALG.

4. Under SIP ALG, enable the Off option.

5. Finally, click Apply and log out.

Sercomm Router:

To disable SIP ALG on the Cosmote router, follow the process shown in the image below.

After logging into the router using its IP address, follow these steps:

1. Select the Internet tab.

2. Open the Advanced Settings submenu and then Security.

3. Select ALG.

4. Under SIP ALG, disable the checkbox.

5. Click Save and log out.

US Robotics Routers:

1. Download the putty.exe application to your computer from this link. The application is free and does not require installation. Save it to your Desktop.

2. Run putty.exe. In the window that appears, enter your router’s IP address in the Host field, e.g. “192.168.1.1” (without quotation marks).

3. Under the Host field, in the Connection Type section, select Telnet.

4. Click the Open button.

5. Enter the Username and Password identified during preparation (enter the username first, press Enter, enter the password, then press Enter again).

6. Type the following commands exactly as shown, pressing Enter at the end of each line:
   siproxd disable
   save
   reboot

7. Restart your router and any VoIP devices you are using. The SIP ALG feature, which was causing communication issues, will now be disabled.

Thomson & Technicolor Routers:

For the majority of Thomson routers and the Technicolor TG582n PRO, TG582n SB, TG589vn V3 models:

1. Download the putty.exe application to your computer from this link. The application is free and does not require installation. Save it to your Desktop.

2. Run putty.exe. In the window that appears, enter your router’s IP address in the Host field, e.g. “192.168.1.1” (without quotation marks).

3. Under the Host field, in the Connection Type section, select Telnet.

4. Click the Open button.

5. Enter the Username and Password identified during preparation (enter the username first, press Enter, enter the password, then press Enter again).

6. Type the following commands exactly as shown, pressing Enter at the end of each line:
   connection unbind application=SIP port=5060
   saveall
   exit

7. Restart your router and any VoIP devices you are using. The SIP ALG feature, which was causing communication issues, will now be disabled.

For Technicolor TG589vac, TG589vac v2 and TG588v v2:

1. Open a web browser (e.g. Firefox, Chrome) and navigate to 192.168.1.1 (default IP address).

2. In the top right corner, click Login. The default username is admin and the default password is admin.

3. Modify the URL so that it includes debug=1 at the end. The address should look like this: http://192.168.1.254/?debug=1.

4. Scroll down and click on NAT Helpers.

5. Toggle the SIP option to disable it and click the Close button.

6. Close the browser and restart your phone. SIP ALG is now disabled.

TP-Link Routers:

If your device interface looks like the one shown in the image below, follow these steps:

1. For Routers with Advanced Setup:

   • Select Advanced Setup.

   • Open the NAT Submenu.

   • Select ALG.

   • In the ALG menu, disable the SIP Enabled option.

   • Click Save/Apply.

2. Alternative Procedure:

   • Download the putty.exe application from this link. The application is free and does not require installation. Save it to your Desktop.

   • Run putty.exe. In the new window, enter your router’s IP address in the Host field, e.g. “192.168.1.1” (without quotation marks).

   • Under the Host field, in the Connection Type section, select Telnet.

   • Click the Open button.

   • You will be prompted to enter the Username and Password identified during preparation (enter the username first, press Enter, enter the password, then press Enter again).

   • Type the following commands exactly as shown, pressing Enter at the end of each line:
     sh
     rmmod nf_nat_sip.ko
     rmmod nf_conntrack_sip.ko

   • Restart your router and any VoIP devices you are using. The SIP ALG feature, which was causing communication issues, will now be disabled.

D-Link Routers:

• Open a browser (e.g. Firefox, Chrome) and enter your router’s IP address (e.g. 192.168.1.15).

• Log in using your router credentials.

• From the management panel, select Advanced Settings and then Application Level Gateway (ALG) Configuration.

• Disable the SIP option.

Netgear Routers:

• Open a browser (e.g. Firefox, Chrome) and enter your router’s IP address (e.g. 192.168.1.15).

• Log in using your router credentials.

• From the management panel, select WAN Settings and then Application Level Gateway (ALG) Configuration.

• Disable the SIP ALG option.

Zyxel Routers:

• Open a browser (e.g. Firefox, Chrome) and enter your router’s IP address (e.g. 192.168.1.15).

• Log in using your router credentials.

• From the management panel, select Settings > Network and then Application Level Gateway (ALG).

• Disable the SIP ALG option.