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Main site to remote site DNS problem via VPN tunnel

Posted on 2008-10-26
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Last Modified: 2010-05-18
This weekend my Data Center was moved from one location to another.  The old location is now a branch office of the new location.  All the servers are at the main location, domain, dns, dhcp ect.  The only thing that remains at the branch location is a ASA firewall, switch and some thin clients.  A vpn tunnel was created between the ASA at the main and the ASA at the remote.  The remote site is getting DHCP addresses from the ASA and the main site is getting DHCP from the DHCP server.  The addresses are not the same.
Ideally, I want both sites to get all of the DHCP and DNS information from the main site.  Is that possible and if so how?
If that isnt possible can I configure my DNS servers to resolve the hostnames from the branch sites ip addressing scheme?
We go live in the morning so help is much appreciated as soon as possible!
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Question by:Jennifer1024
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by:hfraser
ID: 22809185
Are the thin client' servers also being hosted remotely? If so, the processing's being done remotely, and the actual address of the clients really doesn't matter. As such, you might as well leave the situation as is letting the local ASA firewall issue the addresses.

One thing to keep in mind, though, is the scope.  If you have many sites, remote sites confgured the same way, you'll want to ensure that each issues different addresses.

The main reason for leaving the address issued locally is to eliminate the need to allow broadcast traffic across the VPN (DHCP requests are a boradcast)
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by:Jennifer1024
ID: 22809280
There isn't a server at the remote site.  Just a switch and the ASA.  Right not neither site can really talk to the other as the addresses are not being resolved.
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by:hfraser
ID: 22809475
OK. So modify the DHCP server in the ASA firewall to point clients DNS to the main site and manage DNS stuff from there. I'd still leave the remote clients getting addresses from the local firewall.
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by:RGRodgers
RGRodgers earned 200 total points
ID: 22809509
This is complex.  But, to do what you say you want, you need to make sure that the firewall is allowing DNS and DHCP communication to pass.  This includes ports 53 (TCP & UDP) for DNS and 67 (UDP) and 68 (UDP) for DHCP.  Others may be required, depending upon your configuration.  Check a list such as
http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers

I also suggest that you use equipment within the remote site to serve DHCP addresses, at minimum.  And, then configure the DHCP server to provide the appropriate DNS server addresses to the client.  

Good luck.
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by:RGRodgers
ID: 22809525
This refereence can provide a lot of help if you can use it:
http://en.wikipedia.org/wiki/Dhcp
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by:Jennifer1024
ID: 22809530
I modified the DHCP server on the remote ASA to point DNS queries to my DNS servers at the main.  I also set up DHCP relay to my DHCP servers.  So far I'm not seeing any difference and the ARP table on the remote ASA still shows old addresses.
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by:Jennifer1024
ID: 22810946
Update:  I forged ahead with different IP addresses at the remote site.  Many of these clients are connecting through thin clients or can connect with RDP so that works fine.  They can connect to the TS at the main site without any issues.  However, I'm having a hard time printing from the TS server back to the remote sites printers.  The printers have new addresses as well and install fine on the server but no luck there either.
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hfraser earned 300 total points
ID: 22811117
Ahh. So there remote site doesn't just have the ASA firewall, a switch, and some thin clients. The printers have addresses that are important.

You have a couple of choices. You can reduce the address range assigned by the ASA DHCP server and assign one of the none-DHCP addresses available to the printers. Or you can reserve the addresses in the DHCP server, which ties an IP address to the MAC address of the printer NIC. The only caveat with this is that if the printer or its NIC is replaced, the reservation fails.

The address has to be in the local subnet to be visible to the servers through the tunnel.

In either case, make an entry in the DNS to reference the printer.
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