Cisco ASA 5500 device DNS server failover settings

[seansobey]

This morning my site had our primary DNS go down, we have 3 DNS servers in the DNS settings tab on all our nics, we have 5 subnets associated to our site. Now when our primary DNS went down we here at our main site were still able to resolve both internal and external, however one subnet range was isolated no internal or external. This subnet range gets there DHCP and DNS Server settings from a Cisco ASA 5500 device series.

No workstations were rebooted at this time, all workstations getting these same settings via Microsoft failed over to the second DNS server in the list.

My question is this, why didn't the cisco ASA 5500 series device move down to the second DNS server and as such restore access? Is it suppose to dynamically go down the list if the primary went down? If I need to to re-write the cli statement then how would I need to state it?

[Vibhor Amrodia · Accepted solution]

Hi,

So , which DNS settings are you referring to ? The DNS being pushed using the ASA DHCP server ?

If yes , the DNS reachability is not checked by the ASA device but by the PC.

ASA only uses DNS when it has to lookup the Domain Name for it;s own use. For ex:- FQDN acl etc.

If the Primary DNS does not work , it automatically moves to the next one.

Thanks and Regards,

Vibhor Amrodia