We have several
ASA 5505 deployed. Currently, we have a setup where the local ASA is answering DHCP queries and is configuring clients with two DNS servers: our DR site DNS server (we use AD) and a public DNS.
We need to give clients access to "the internet" when the VPN tunnel is down (this means not only packet routing but DNS answers), which rules out serving DHCP from our side. The above config allows us to use
vpnclient server [Production site VPN target] [DR site VPN target] without issue.
This is a workaround from previous config where we manually failed over tunnels by adjusting the DHCP assigned DNS. Super high touch and slow.
On a Fortigate, there was a load balancing service that would create a VIP and had some checks ot verify connectivity to DNS servers.
Beyond a creative solution like load balancing, how can we configure clients that are assigned DHCP by our field ASAs to send DNS lookups to specific servers?
Just thought that we might use load balancers at each site that serve DNS via the same VIP (only accessible by VPN clients). But this is a complex server-side solution for a possible client-side problem.