This seems so common, I must not be using the right search terms. Basically, I want to change openwrt (all three routers dir-878);
have two WANs (no soldiering just software). the two WANS will be called cable modem and isdn
traffic will use cable modem when working or fail over to isdn
XBOX and Zoom laptop always use isdn or fail over to cable modem
Basically all traffic goes to cable modem except for XBOX and Zoom laptop which goes to isdn. Obviously if isdn or cable modem goes down all traffic uses the internet provider that is working.
I think I can "tag" or QoS all traffic from a network mac (not apple laptop) address and then openwrt will route that to isdn or fall back to cable modem some how....
Once you install OpenWrt, you can actually collapse the network down to a single router (or at least a single one of those devices doing active routing)... if you need additional APs, you can use the other 2 units in the dumb AP configuration.
Meanwhile, you'll use mwan3 to setup the multiple wans, and either that or policy based routing achieve the specific lan > wan mappings you desire.
Thank you. I think mwan3 will do the fail over. I am not sure how to mark traffic from mac address A on network1 to tell the last router with mwan3 + internet modems to specially do an exception routing. E.g. Xbox on network 1 will always through telecom since it has lower pings and not use cable modem.