Multicast

In my previous post, we hit a wall with the kernel’s multicast forwarding logic. The core issue was the RPF (Reverse Path Forwarding) check failure for sources on unroutable networks. While digging deeper into this, I found it’s a well-documented challenge in multicast literature, often called the “…

Many consumer and industrial devices—from home security cameras to the HDMI-over-IP extenders I investigated in a previous post—are designed as simple appliances. They often have hard-coded, unroutable IP addresses (e.g., 192.168.1.100) and expect to live on a simple, isolated network. This becomes a major problem when you need to get their multicast video or data streams from that isolated segment to users on a main LAN. My goal was to solve this with a standard Linux server, creating a simple, high-performance multicast router without a dedicated, expensive hardware box.

Can a standard Linux server act as a simple, kernel-native multicast router for devices with hard-coded, unroutable IP addresses? This article chronicles an investigation into combining nftables SNAT with direct control of the Multicast Forwarding Cache (MFC).