How to properly do failover on 2 Dialer interfaces

[Jamesits]

I have an ISR 1000 series router (IOS XE 16.9) connected to 2 PPPoE lines to 2 ISPs. Dialer0 is slower but more steady, Dialer1 is faster but fails every few days (BRAS will fail to authenticate for some minutes). I want to build a failover mechanism so if Dialer1 is working then everything goes to Dialer1, and when Dialer1 is down everything should go to Dialer0. The question is, when Dialer1 fails, the interface is still up without IP, so the routes to it will not be disabled. How to correctly do failover in this situation?

Here's what I've tried but failed:

1. Two routes with different metric

ip route 0.0.0.0 0.0.0.0 Dialer1 10
ip route 0.0.0.0 0.0.0.0 Dialer0 20

As stated above, Dialer1 will not go down but in a status of up and no IP assigned so the upper route will still in effect, dropping all the traffic.

2. ip sla

ip route 0.0.0.0 0.0.0.0 Dialer1 10 track 1
ip route 0.0.0.0 0.0.0.0 Dialer0 20
ip sla 1
 icmp-echo 8.8.8.8 source-interface Dialer1
 threshold 1000
 timeout 1000
 frequency 3
ip sla schedule 1 life forever start-time now
ip sla enable reaction-alerts
track 1 ip sla 1 reachability

Although I have set source-interface Dialer1, it seems still going out from the default route, thus creating an oscillate situation (every second the route switches between Dialer0 and Dialer1). 

[paul driver]

Hello

Your ipsla config is pointing to a internet address which may be still be seen as accessible by your router so your sla wont initiate and failover correctly, try and monitor an ip address that is closer to the dialer 1 interface.

Another alternative is implement dailer-watch setup but as your using static routes no so sure it would work accordingly

[Jamesits]

Hi, I don't really understand here, why I have set the source interface but the packet is still going out of another interface? I thought source interface meant source interface...

My PPPoE interfaces will get random IP ranges from my ISP so pinging an IP address very near is virtually impossible.

[Jamesits · Accepted solution]

I found the way to do this correctly. There is a function in track which can see if there is an IP on the interface and set track status accordingly.

Full config:

track 1 interface Dialer1 ip routing
ip route 0.0.0.0 0.0.0.0 Dialer1 10 track 1
ip route 0.0.0.0 0.0.0.0 Dialer0 20