With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
cdcDNSServerAddr
Cisco DNS Client DNS Server Address
1.3.6.1.4.1.9.9.436.1.1.4.1.3
This object represents the address of the DNS Server. This object is a mandatory object for row creation. An attempt to modify this object will fail with an 'inconsistentValue' error, if the value of the corresponding instance of 'cdcDNSServerStatus' object is active(1).
Back to CISCO-DNS-CLIENT-MIB MIB page.
IPHost Network monitor allows you to monitor cdcDNSServerAddr on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco firewalls right now.