The vital role of security settings in VoIP

Understanding SIP ALG and its impact on business phone systems

Voice over IP (VoIP) has become the go-to solution for business phone systems. It offers cost savings, flexibility, and a wide range of features that enhance communication and collaboration. However, it’s crucial to prioritise the security of your VoIP infrastructure to protect sensitive business information and maintain uninterrupted service.

We find that Session Initiation Protocol Application Layer Gateway (SIP ALG) settings are often overlooked, and although they were originally created for great cause, many VoIP providers suggest switching them off (as does Wanatel). Sometimes these settings impact the integrity and reliability of customers’ business phone systems.

Understanding VoIP and SIP:

VoIP enables voice communication over the internet, replacing traditional telephone lines with data packets. It uses Session Initiation Protocol (SIP), a signalling protocol that establishes, modifies, and terminates VoIP calls. SIP plays a vital role in managing the communication flow between various endpoints, including IP phones, softphones, and SIP-enabled devices.

So what is SIP ALG?

SIP Application Layer Gateway (ALG) is a feature present in many network devices, such as routers and firewalls, that assists in the implementation and translation of SIP messages. It aims to overcome network address translation (NAT) issues by automatically modifying SIP packets and opening or closing specific ports. SIP ALG can be both a helpful tool and a potential vulnerability, depending on how it’s configured and the network environment.

Proper SIP ALG Configuration benefits

NAT Traversal

SIP ALG allows SIP packets to traverse through NAT devices, ensuring seamless communication between internal and external network devices. It helps overcome issues related to private IP addresses and firewall settings, enabling successful call setup and audio transmission.

Quality of Service (QoS)

Appropriate settings for your SIP ALG can prioritise voice traffic over other network data, improving call quality and reducing latency. By applying appropriate QoS settings, businesses can ensure reliable voice transmission and enhance the overall user experience.

SIP Header Manipulation

It is possible that SIP ALG can modify SIP headers, enabling advanced call features and compatibility with certain SIP implementations. It allows for functionalities like call transfer, call recording, and call waiting, enhancing the capabilities of your VoIP system.

Beware of these potential security compromises

Protocol Interference

Improperly configured SIP ALG settings may interfere with the SIP protocol, leading to call failures, dropped calls, or audio distortions. It’s crucial to test and validate the impact of SIP ALG on your specific network environment before enabling or disabling this feature.


SIP ALG implementations have been known to introduce security vulnerabilities, potentially exposing your business phone system to attacks such as SIP-based exploits, toll fraud, and eavesdropping. Attackers can exploit weaknesses in SIP ALG to bypass security measures or intercept sensitive communications. Regularly updating firmware and implementing strong security practices are essential to mitigate these risks.

What is SIP ALG best practice in VoIP?

Note for all Wanatel resellers it is highly recommended to disable SIP ALG.

  1. Evaluate

Understand your network infrastructure and determine whether SIP ALG is necessary. Test its impact on call quality and reliability. In some cases, disabling SIP ALG may be the preferred approach to avoid potential security vulnerabilities.

  1. Firewall Configuration

Configure your firewalls to allow SIP traffic while implementing appropriate security policies. Whitelist trusted IP addresses, enable encryption, and regularly monitor for any unauthorized access attempts.

  1. Regular Updates and Patches

Stay up to date with firmware updates for your VoIP devices and ensure they include security patches. Regularly monitor vendor advisories and apply recommended fixes promptly to address any discovered vulnerabilities.

  1. Secure Authentication

Implement strong passwords and enable two-factor authentication for user accounts. Restrict access to SIP services based on IP addresses and employ secure transport protocols such as Transport Layer Security (TLS) for signalling and Secure Real-time Transport Protocol (SRTP) for media encryption.

Most importantly, ask your VoIP provider to check that SIP ALG is properly set up for your environment. As businesses increasingly rely on VoIP for their communication needs, ensuring the security of these systems becomes paramount. Configuring SIP ALG settings properly and understanding their implications is a crucial step towards achieving a secure and reliable VoIP infrastructure.

If you have VoIP concerns, or would like advice on your VoIP setup, reach out to one of our Wanatel experts today. By following best practices, regularly updating firmware, and implementing robust security measures, businesses can protect their sensitive data, maintain uninterrupted communication, and maximize the benefits of VoIP for their operations.