@Freddo I don't know, there is probably something wrong with the ASA configuration, have you tried the cisco forum :-) I did a trace here but I don't have an ER605 in front.. I have this software...

Have you configured dns on your ASA ? Try ping somthing with name from console on your ASA or configure ASA dns with this command dns domain-lookup outside DNS server-group DefaultDNS name-server...

@Dixon_Herize Try and update your firmware on the router and controller if you use that.

@Freddo If you use /31 mask 172.16.50.14 172.16.50.15 is only network and braodcast address try /27 (255.255.255.224)

@Freddo Cisco ASA doesn't have load balancing, I don't know if it works that well on TP-Link either, but I don't understand why you want to set up failover on Cisco ASA if you're going to use the...

@Freddo If I understand you correctly, you want to use an ER605 in front for WAN failover, isent it easyer with WAN failover on Cisco ASA,