HEADS UP: PPP WAN (PPPoE, L2TP, etc) default gateway changes
I believe I located the source of the trouble with default gateway switching and PPP style WANs. With "set iface route default" in the mpd config, it was removing the default route when the PPP link was lost even when it did not match what it put in place. I omitted that line and put a safety belt in ppp-linkdown to stop it from removing the gateway when it doesn't match.
I tested this with default gateway switching on and off, by rebooting, manually disconnecting the PPP link, and manually disconnecting the NIC link, worked each time, though still possible some issues remain. Feedback appreciated.
Before this fix, if a PPP WAN was the default gateway, the automatic switching would fail (it would work for a moment, then die, and might come back if something tickled the gateway code right), now it should flip immediate as soon as the default gw goes down and flip back when it recovers.
Thanks for the Heads Up. Don't have any PPP connections but I updated/gitsynced and tested: Default Gateway Switching with two static GWs still works fine.