If the router is filtering too, ubuntu has to be aware of the gateway's existence for both interfaces and use table and rule settings for a correct routing.
Normally, a Linux system only has one routing table, in which only one default gateway can make entries. With iproute2, you have the ability to setup an additional routing table, for one thing, and allow this table to be used by the system based on rules, for another.
linux networking homelabThis buildĀ is not about building the biggest, baddest, and most redundant server we can build, rather this oneĀ is about building the biggest and baddest server that we cram in to a 1U case that is only 19ā wide by 12ā deep.
homelab server howto