DSL main, cheap little LTE modem via USB as a fallback. Both are connected to my OPNsense as a gateway group. Failover happens after 5s of full packet loss (and a bunch of less aggressive failover conditions, latency etc.). That of course changes my public IPv4 address, so yes this drops existing connections. Not a big deal for most stuff, Netflix reconnects quickly enough that this isn't even noticeable. For the stuff where the connection can't drop like that, I run a VPN tunnel on each of the two uplinks to a small relay box with a static IP sitting in a datacenter. When DSL fails, the traffic is routed through the other VPN link but comes out of the relay box with the same public IP.
DSL main, cheap little LTE modem via USB as a fallback. Both are connected to my OPNsense as a gateway group. Failover happens after 5s of full packet loss (and a bunch of less aggressive failover conditions, latency etc.). That of course changes my public IPv4 address, so yes this drops existing connections. Not a big deal for most stuff, Netflix reconnects quickly enough that this isn't even noticeable. For the stuff where the connection can't drop like that, I run a VPN tunnel on each of the two uplinks to a small relay box with a static IP sitting in a datacenter. When DSL fails, the traffic is routed through the other VPN link but comes out of the relay box with the same public IP.