What is SIP ALG / SIP Inspection?

SIP ALG

SIP ALG is a feature found in some routers and firewalls that helps with making phone calls over the internet. When you make a phone call using a service like VoIP (Voice over IP), the information about the call is sent using a protocol called SIP.

Now, when you connect multiple devices to the internet using a router, it assigns them private IP addresses. These private IP addresses are not directly accessible from the internet. To allow the devices to communicate with the outside world, a technique called Network Address Translation (NAT) is used.

SIP ALG comes into play when you want to make phone calls from devices behind a NAT router. It helps translate the information in the SIP packets so that the call can go through the router correctly. It changes the IP addresses and ports in the packets so that they can pass through the NAT and reach the other end of the call.

However, SIP ALG can sometimes cause problems. It may not work well with certain devices or services, causing issues like dropped calls or one-way audio. In such cases, it's often recommended to disable SIP ALG in the router settings.

SIP Inspection

SIP Inspection is a security feature found in some firewalls. When you make phone calls over the internet, the communication between your device and the other party goes through various network devices, including firewalls.

SIP Inspection is like a security guard that watches the phone call traffic passing through the firewall. It looks at the information in the SIP packets to make sure everything is safe and secure.

Its main job is to detect and prevent any malicious activities or attacks that may target the phone call system. It does this by analyzing the SIP traffic and checking for any suspicious patterns or signs of an attack. If it finds something harmful, it takes action to protect your network, like blocking the suspicious traffic or alerting you about it.

SIP Inspection adds an extra layer of security to your phone call system by actively monitoring the traffic and keeping an eye out for any potential threats.