When a wan link is considered failed?

[burn]

For multiwan setup, how exactly does pfsense determine if one of uplinks failed? Is there any setting for this?

[GruensFroeschli]

You set a monitor IP.
When the monitor IP is no longer reachable, the link is considered down.
On 2.0 you can set more criteria like, high latency, a certain amount of frame drops

[Lemzip]

so if the pppoa or pppoe sessions drop, the pfsense will still show the link as up as esentially the internal ip is still responding to ping

[GruensFroeschli]

If this is the case you chose your monitor IP wrong.