Hi,
Well, that’s exactly what I have done, isn’t it? Except in my MWE ISP2 does not use PPPoE and thus has a DHCP startup script.
The objective is to keep it simple to achieve efficiency/simplicity and reduce chances of failure/issues later on if you decided to add more complicated policy routing/load-balancing, whatever.
Obviously. But again, what you are doing is not equivalent to what I am doing, is it? I totally agree that this is all a delicate trade-off balance. In your solution, if ISP1 fails, attached clients have no way to reach 8.8.8.8 or 1.0.0.1. This is avoided in my solution at the price of slightly more complex routing. Obviously, whether the trade-off is worth it is something that everybody has to decide individually (and, in fact, I am not certain myself, but I wanted do get it to work).
Arguably, your code is more complex than really necessary (provided that ISP 2 is just a backup link anyway and not meant to do load-balancing, as I have assumed and explicitly stated in my example). In that case, I don’t see any benefit to be gained from actively checking whether the ISP 2 uplink is actually up and running because there is nothing you can do about it anyway, so you could just as well just leave out all the checking via 8.8.4.4 and 1.1.1.1. That would simplify your setup as well.
(As a side note, my MWE is somewhat longer because I actually included all relevant configuration aspects, not just parts. These missing but crucial config lines cost me the the better part of two days to figure out. I think it is much better to include everything that is necessary to actually reproduce something and, also, state assumptions explicitly.)
Cheers,
Toby.