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Cannot ping external IP/web address from LAN, yet can access site fine

Posted on 2009-03-31
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Last Modified: 2012-08-13
Embarking on a trip down the rabbit hole that started with Wordpress but is ending up with crazy DNS issues - hoping someone can help! My LAN network is set up with a Windows 2003 box which hosts DNS, a 10.5.6 Mac server which hosts our website, DHCP, and other various things, all behind a Netgear FVX538 firewall box.

The Mac server hosts our Wordpress website - recently I had been trying to start hosting a podcast for the Wordpress blog. Wordpress normally supports auto enclosures of media files, but that wasn't working, which I thought was strange. After much searching and testing, I realized that something was amiss with DNS that was most likely causing the issue.

I can ACCESS my website from the LAN (both on the server it's being hosted from and other computers in the LAN) but PINGING either the external IP or the domain name doesn't work. It pings for one entry, spits back the IP address, then stops with no other error message or notification of any kind. I can ping other external sites just fine, and can ping internal IP addresses just fine as well.

I'm not sure if this is a DNS problem, although it seems safe to say that it is. And because I've noticed no other issues, I'm not really sure where to begin in figure out what the problem is. It seems that there's some issue going on with internal DNS, so if anyone has advice of what I should look for, please let me know!
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Question by:topher1078
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by:Chris Dent
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If you're getting the correct IP Address back in response to a request for a name then DNS is done and out of the picture.

However, your server is hosted inside your network in this scenario?

That is you have something like this:

Internet   -----   Router   -----   Switch   -----   Clients
                                                     |
                                                Server

And you use NAT to get a public IP address from outside your network to your Server?

If so, then  no, clients will not be able to access the server using the public IP (and therefore also won't be able to using the public name which presumably resolves to that IP). If that is true, do you have a DNS server inside your network as well?

Chris
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by:topher1078
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That diagram is basically what we have. I have the router/firewall box set up with the ISPs DNS server, then an internal DNS server hosted on the Windows 2003 box. And yes, my firewall is using NAT to get outside the server.
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Chris Dent earned 500 total points
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Okay, so clients inside won't be able to access on the public IP because it just gets horribly confused trying to route the requests.

The traditional answer is to create a zone on the internal DNS server that will provide clients inside the network with a private IP address for the domain name in question. This only works if all your internal clients use that internal DNS server.

I've blogged about this in the past, so I hope you'll forgive me pasting the link rather than rewriting my instructions for it :)

http://www.highorbit.co.uk/?p=459

Chris
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by:topher1078
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I will try those instructions - thanks - but I may have figured out something else. Tried switching out the Netgear firewall to our old Symantex VPN/100 and lo and behold, everything started working again - enclosures, pinging, the whole nine yards. So I guess when I was setting up the Netgear I missed a setting, any thoughts as to what that might be, or should I do your DNS suggestions first (with the Netgear) and see if that works first?
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by:Chris Dent
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Some routers will handle it, some won't. It also depends if your server is set up in a DMZ.

The most important part is that it works from the public networks, it is possible to work around any issues internally.

Chris
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by:topher1078
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Followed your DNS instructions and everything now works great, with the new router. Thanks so much!
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