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Old 08-18-2017, 07:07 PM   #1
des_a
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Virtual Server to Virtual Server: Connection Not Working?


I probably cannot actually get it to work, but I just wanted to see if I had an explanation of why it wouldn't work.

I am using Virtual Box on Windows 10. I am running 4 virtual servers on it. One is vmain. vmain has my DNS server on it. My DNS server only resolves my internal names. I only have one name on the outside, which is done by dynamic DNS. I also only have one public IP. The rest are behind mainrouter and/or other routers. vmain runs Mandriva Linux 2010.1.

I also have as one of the servers, an application server vwinxp. It is exactly that, an application server. Users can log onto it to run programs that are not possible to run any other way, or are more convienient to have there.

From vwinxp, I cannot seem to access any website services on vmain by their DNS name. But those which are accessible by the external DNS name, I can access. Each virtual server, has it's own static IP in mainrouter, but these 4 are located on the same physical machine, which in turn has it's own static IP.

Why is this? Is there a reason I cannot access by internal DNS names? Does it, like I suspect have something to do with looping? I doubt I can fix it, but if I can, how would I go about it, without locating each server on separate machines?
 
Old 08-18-2017, 10:02 PM   #2
jlinkels
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It seems to me that vwinxp does query the external DNS, but not the DNS on vmain.

How did you set up the DNS in vwinxp? I am not sure if you set 2 DNS (the external one and vmain) that it will quiry both. I also assume you have vmain as caching DNS server. So vwinxp must only query vmain and nothing else.

Do you have a program like dig on Windows? So you can see who answers the DNS queries.

I also assume all your NIC on the VMs are bridged. VB does NAT by default.

You can also run tcpdump on vmain to see if DNS queries from vwinxp are received.

jlinkels
 
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Old 08-19-2017, 05:36 PM   #3
des_a
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I set up static IPs through DHCP. Yes, everything is bridged. My DNS setup is a bit tricky. Here goes a simple explanation of it:

* Everything gets the DNS servers from DHCP
* vmain is the DNS server
* OpenDNS is the secondary DNS server for DHCP to give out
* vmain has OpenDNS as the first external DNS server
* vmain has Google Public DNS as the secondary external DNS server
* vmain has my ISP's DNS as the last external DNS server
* For internal queries in my network, it will query vmain and get the answer from there
* For external queries, such as Google, it will get the address from the external DNS servers, in the order previously specified
* DNS is NOT publicly accessible
* DNS is setup to be a LAN service, not accessible from the Internet
* DNS was setup using drakwizard, then webmin for the vmain portion
* There is no public registry of my DNS names. So even if it were publicly accessible, unless you pointed things to my DNS server to use it specifically, you could not resolve the internal names from the other machines on the Internet. I don't want to pay and can't pay for the registration.
* From the outside, I have a NO-IP Dynamic DNS name
* I have a public dynamic IP address
* All of the inside addresses are static, except for some in the guest subnet or certain types of other guests
* The internal names are mapped to internal addresses
* The Dynamic DNS name is mapped to the public IP

I have no idea what a cacheing name server is, so I don't know whether mine is that way or not.
 
Old 08-19-2017, 05:37 PM   #4
des_a
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Quote:
Do you have a program like dig on Windows? So you can see who answers the DNS queries.
I have the program ping and the program nslookup, or at least I think that is what the second one is called...

I will try both of them and see what happens.
 
Old 08-19-2017, 05:51 PM   #5
jlinkels
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nslookup is the right tool. In Linux it has been superseded by dig. But when I wrote the post I could not come up with the old name. Yes, nslookup is a valueable tool.

A caching nameserver is a DNS which servers local domains, and if the domain is external, it resolves from the specified external DNS. Once it has resolved the external name, it keeps it in cache for some time so future requests are handled faster. It sounds complicated but it is totally transparent to the user.

Bind9 is such a DNS. And I doubt if it has something to do with your installed DNS. Your installation looks right.

As vwinxp is only able to resolve the host which has a publicly visible DNS name it seems like vwinxp skips the internal DNS.

You have the vwinxp and some more virtual machines so you might want to compare results from nslookup on the vwinxp and the other virtual machines.

jlinkels



jlinkels
 
Old 08-19-2017, 05:58 PM   #6
des_a
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This "could" indicate an error. I am checking it out.
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Old 08-19-2017, 06:09 PM   #7
des_a
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Here is the setup of the DNS servers on vwinxp.
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Old 08-19-2017, 06:10 PM   #8
des_a
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I still don't understand what a cacheing nameserver is from that description. Please simplify.
 
Old 08-19-2017, 06:12 PM   #9
des_a
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Here is nslookup from vmain
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Old 08-19-2017, 06:18 PM   #10
des_a
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nslookup from vwinxpsrv. Seems like a Windows XP thing? DNS of vwinxp looks right...
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Old 08-19-2017, 06:20 PM   #11
des_a
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tcpdump not installed, I guess...
 
Old 08-19-2017, 06:23 PM   #12
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A caching name server looks up external addresses on the external DNS. Once it has found the address it is kept in cache. Future lookups are served from cache and faster. If the address is internal the name server serves them from the local database.

Your post #6 indicates a problem. I don't know the algorithm XP uses for determining which DNS server it uses. The next logical step is to set vmain as *only* DNS for XP and see if local names are resolved.

jlinkels
 
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Old 08-19-2017, 06:57 PM   #13
des_a
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This seems to solve the problem. The only problem as far as I can tell with this, is that if vmain fails, Internet will then completely stop working instead of as designed, going into reduced functionality mode, gradually as DNS servers fail. What would be the next step after that? I used to have a router that would allow you to have it appear as if the router was the DNS server, but it still did my trick to ensure reduced functionality modes in the event of failure.

DD-WRT MUST somehow allow you to do this too, I just don't know which settings to use. Maybe if I did that, it would fix the problem? Then clients would be served one DNS address, the router's internal address. Then the clients would get that address, but in the background it would do my "trick". Maybe that would work?
 
Old 08-19-2017, 06:58 PM   #14
des_a
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P.S. - I understand what you mean by cacheing now. I think it is such as server.
 
Old 08-19-2017, 07:46 PM   #15
jlinkels
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I would first make a risk analysis. Your case it that vmain stops working. While vwinxp remains working and you want to keep that functionality. Condition for that is that both Win10 and Vbox remain working as well, just vmain is failing. If you have vmain on the same datastore (hardware storage) as vwinxp, I think vmain will not fail easily on its own. (My problem with some of my Linux servers is that I forget where they are. Seriously. Because they never fail and I never have to access them)

Second option: install the same DNS on another Linux box (or VM) and sync the databases. (Don't ask how in OpenDNS. I know it can be done in Bind9). Then you *can* point the 2nd DNS in windows to the other Linux box. This box contains the same DNS records as vmain. WinXP gets the same reply from both DNS-es to will resolve correctly.

jlinkels
 
  


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