Multiple ISP for Failover

[pbxnkey]

I am setting up an ASA 5505 with multiple ISP connections for Failover. My question is related to the ISP DNS Servers.
I am using the ASA to hand out DHCP to the LAN. I know I can assign dns servers either globally or through the DHCP scope but it limits me to only 2 DNS Servers.
This is what I have tried:
ciscoasa(config)# dhcpd dns 4.2.2.2
ciscoasa(config)# dhcpd dns 4.2.2.2 8.8.8.8 interface inside
dns domain-lookup outside
dns server-group DefaultDNS
name-server 4.2.2.2
name-server 8.8.8.8

If the ASA Fails over I want the LAN devices to use the ISP's specific DNS Servers? Is that possible or do I have to use the same dns server?
Thanks.

 

[hairlessupportmonkey]

I didnt think the 5505 had fail over capabilites? I know you can do a multiwan licence, but its techincally doesnt fail over?

ACSS - SME
General Geek

 

[pbxnkey]

If you use ipsla to monitor the primary WAN gateway and have a weighted static route to the secondary WAN gateway it will fail over.

 

[iggsterman]

If I understand you correctly you will have 2 ISP links connected to the same ASA and will have tracked route path failover? If so, you will not be able to use ISP-specific DNS server IP addresses in your DHCP handoff because there's no mechanism to switch them when your path changes. The primary ISP would deny DNS requests coming from a "foreign" subnet, and visa versa.
Another way to handle this wold be to configure a small DNS server inside your LAN and give its IP address to DHCP clients, which would make you independent of ISP DNS services.

 

[pbxnkey]

Unfortunately a DNS Server won't be possible. It's a small site. The only alternative that I see is to use google dns.