I'm not sure if the title correctly describes the problem.

We have websites setup on our sbs 2008 machine that are publicly available via an external address and internally available via an internal address. The external addresses are different sub domains with a domain. Eg http://site1.domain.com and the internal address is http://site1.

Over the weekend the public addresses stopped working when viewed from inside our network but viewing them from a machine outside of our network works fine.

The internal addresses mapped to the same sites still work fine internally and obviously can't be resolved outside.

When i do a ns lookup or ping the addresses they resolve the correct ip address from inside our network. I've cleared the DNS cache, restarted the DNS server but they still don't load up.

I'm stuck what to try next. I'm not sure what has changed over the weekend, I certainly haven't done anything.



Internal clients can resolve http://site1 to INTERNAL_IP and the page loads. External clients can resolve http://site1.domain.com to EXTERNAL_IP and the page loads. Internal clients can resolve http://site1.domain.com to EXTERNAL_IP but the page does not load.

The above statements are the norm for most web servers. It sounds like what you want is...

Internal clients to resolve http://site1.domain.com to INTERNAL_IP.

This will allow your internal users to use the same URL as external users. To accomplish this, just add a record to internal DNS reflecting site1.domain.com to INTERNAL_IP.

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  • Otherwise known as split-horizon DNS (serving different information for the same name depending on where the request comes from). In this case you could configure the local DNS resolver with the internal IP and make it authoritative for the domain so internal users get the internal IPs for the same domain as external users access the sites with. – Justin Scott Oct 7 '09 at 2:50
  • the thing is that 1) it was working before without the need for an internal dns record for the full domain and 2) even if I do as you suggest it still doesn't work even though an ns lookup now resolves to the internal ip! what's going on? – Charlie Bear Oct 7 '09 at 9:01
  • firewall/networking issue. something might be blocking port 80 in the middle. – sybreon Oct 7 '09 at 10:01
  • Any tips on how to do this on Windows 2003 Server? I'm a developer and totally new to configuring DNS. – jpierson Feb 4 '10 at 23:22

Check your firewall/router. Chances are, that something has changed between your internal machines and the servers. Try pinging them and tracerouting them. If those work, maybe a router/firewall is blocking port 80 access in between. In a corporate environment, sometime the network admins make adjustments or install new switches without realising some of the new problems it causes.

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  • I've checked and there doesn't appear to be any changes to the router or firewall. Trace routing and pinging from inside the network resolves instantly but the sites don't load in a browser! – Charlie Bear Oct 6 '09 at 11:03
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    Just because you can ping the machines does not mean that you can connect to them if there is some firewall somewhere blocking certain ports. It could be a firewall on the server, on your machine or anywhere in between. Try telnet serverip 80 to see if you can connect directly to that server from different stages in your network. – sybreon Oct 6 '09 at 13:11
  • Also, ensure that the webserver is actually running on the server of course. :) – sybreon Oct 6 '09 at 13:11
  • the web server is running. the internal addresses resovle and you can get to the external sites from outside the network – Charlie Bear Oct 6 '09 at 13:19
  • Yea, have you tried to telnet serverip 80 to see if you can telnet it from your machine? If you can, then it might be a browser problem. Otherwise, it would be a networking problem. – sybreon Oct 6 '09 at 15:18

I suspect you need a Hair-Pin NAT on the firewall Happens a lot in our enviroment When I get problems

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  • More detail might make this a better answer. – Dave M Aug 1 '13 at 16:33

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