I have an 1800 ISR router with an ADSL HWIC. The HWIC is configured and I'm connecting to the provider without any problems. Behind that, I have an ASA firewall coming from an internal interface on the ISR. I have been using the DNS settings provided by my ISP to manually conifgure my client stations on the inside of the ASA and would like to transition to DHCP.
When using the ISPs DSL modem, the modem obtains the DNS information for that session which periodically changes. How can I configure my1800 ISR to get this DNS information, pass it to my ASA, and have the ASA use this information when leasing IPs to clients?