Redundant Internet connections on consumer hardware with OpenWrt and Mwan3
A router with two Internet connections provides many advantages, including better network performance and continued operation if one link fails. Redundant Internet connections have long been standard for data centers and enterprise networks, but they are relatively rare in homes and small offices.
One reason for the absence of redundant connections on small networks is cost, but even when cost is not an issue, home users and small-time admins are often intimidated by the technical issues of supporting two Internet connections through the same inexpensive router.
The ever-resourceful open source universe, however, does provide an inexpensive solution for running redundant Internet connections through an inexpensive home router. The solution begins with OpenWrt, a Linux distribution designed to run on routers and other embedded devices. If you are adventurous enough to install OpenWrt on your router device, you will discover you have much more control over the device than you ever had with the standard router firmware interface. In particular, the Mwan3 extension available for OpenWrt provides support for redundant connections. Mwan3 dynamically manages access via two or more uplinks, uses Ping to ensure that the links are working and, when necessary, adds NAT support and dynamic IPtables rules.
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