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new firewall = internal DNS not working anymore

Posted on 2012-09-06
Medium Priority
Last Modified: 2012-09-11
Hey everyone

I recently put a new firewall in place (a sonicwall tz215) and everything went pretty well--DHCP, internet, etc working, but one thing that went wrong was the DNS no longer worked. It looks like it's the internal DNS server, because when I ping internal servers from inside the network, I get weird external addresses (instead of 192.168.*.*, it's 8.8.something.something.

Anyone have any idea what might be going on here?

Thanks for the input!
Question by:sdcox72

Assisted Solution

Ganpar earned 400 total points
ID: 38374841
Please check diagnostic test dcdiag /test:dns... Is it reporting any error?
LVL 17

Assisted Solution

lruiz52 earned 400 total points
ID: 38374867
Check the dhcp scope on the new firewall, make sure it's assigning the internal dns ip, if not set it, then make sure you have a DNS forwarder to an external DNS like your ISP's dns or dns server).
LVL 39

Assisted Solution

ChiefIT earned 400 total points
ID: 38375094

A firewall/router providing DHCP will by default try to support DNS. It will not register/host the MSDCS records for domain services (hosing up authentication, replication and other domain features)..

Disable DHCP on your firewall/router and put it on a windows based server with all the scope options set correctly. If you already have a Windows server hosting DHCP, it will need to be stimulated after you disable DHCP on the firewall/router. A rogue DHCP server will knock down a windows based DHCP server.
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LVL 19

Assisted Solution

by:Miguel Angel Perez Muñoz
Miguel Angel Perez Muñoz earned 400 total points
ID: 38375278
You must use your internal DNS server to resolve external IP address. Configure DHCP server to lease IP using internal DNS and add a forwarder on your DNS:
LVL 17

Accepted Solution

Brad Bouchard earned 400 total points
ID: 38380199
He doesn't have to switch from the SonicWALL to a server for DHCP.  If you're using the Enhancec OS on your TZ215 then you can setup DHCP to forward DNS to your internal servers.  Leave DHCP on the firewall and point DNS in the firewall to your internal DNS servers.

Author Comment

ID: 38387387
Thanks for the assistance guys -- as it turns out the firewall was dropping packets from the DNS server because it considered it an IP spoof attempt b/c of a miswired switch. Ugh, what a pain.


Author Closing Comment

ID: 38387391
Just giving you all split points based on your willingness to give me help. Thanks again.

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