That seems semitrivial on Android since at least a decade back, you just need to implement it and find all the edge cases, so I guess there is a reason this is

That seems semitrivial on Android since at least a decade back, you just need to implement it and find all the edge cases, so I guess there is a reason this is not done already. e.g . one routing table per interface add rules in global routing table for each new interface that is started: ip rule add from/to $IP_OF_IFACE/32\ table $UNIQUE_RT_FOR_IFACE ip route add default via IP_OF_IFACE_GW/32\ dev $IFACE_NAME table $UNIQUE_RT_FOR_IFACE Then when something changes on the iface that is not defaul; 1. remove old configs for that iface, 2. open a socket on the new ip on that iface to test internet connection. 3. If ok: change default in main routing table to the GW that iface uses.