What are the best network security practices for VoIP systems?

Steps One through five detail some of the more pragmatic protection elements of any computerized domain. The problem with VoIP is the securitization can lead inherently to additional overhead and latency that impacts the time sensitivity of VoIP packets. As such, segmentation of the VoIP portion of the network from the Data portion of the network is well advised. It facilitates dedicated bandwidth to the sensitive VoIP portion of a customer discussion and simplifies the application of QoS or Quality of Service measures that help to ensure that packets aren't dropped with subsequent degradation of Voice Quality, all with the intention of ensuring the security of the system that simultaneously send voice and data over the same infrastructure.

The first line of defense for VoIP security is robust password management. Enforce complex, unique passwords for VoIP accounts to thwart unauthorized access. Regularly update and rotate passwords, minimizing the risk of unauthorized entry.

Data transmitted over VoIP channels must be shielded from prying eyes. Employ robust encryption protocols such as Secure Real-time Transport Protocol (SRTP) to secure voice data. Encryption ensures that even if intercepted, the data remains unintelligible without proper decryption keys.

Regularly update all VoIP software components to patch vulnerabilities and enhance security. This includes the VoIP server, applications, and associated security modules. Automated updates and patch management systems can streamline this process, ensuring timely protection.

To configure a firewall, you first need to identify a list of ports needed for your VoIP system to function properly. You can get this list from the official documentation of your system or via using special tools. For example you can use ss -l4n on Linux systems to identify ports in LISTEN status. But ports that are not in LISTEN status will not be shown up (i.e. RTP port range will not be in the ss command output)

Encryption processes. The location of the encryption process is just as important as the fact that it has been implemented at all. Although firewalls can potentially handle the encryption process, it is often best applied at the SBC or Session Border Controller when utilizing SIP or Session Initiation Protocol as the basis for performing VoIP transmission.

Strengthen access controls by implementing multi-factor authentication (MFA) for VoIP system access. MFA adds an extra layer of security beyond passwords. Additionally, establish clear authorization protocols, ensuring that users only have access to the resources necessary for their roles.

You can use OpenSource tools like Fail2Ban to create custom rules or to use predefined rules. Fail2Ban is like mini-IDS/IPS system. IDS/IPS stands for Intrusion Detection System/Intrusion Prevention System. Fasil2Ban looks through system logs and uses predefined templates to identify malicious activities like wrong password attempt, enormous number of tries etc.