NFS and DNS

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Daniel-A

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So this issue hit me two times, I failed to add to my knowledge base so I ended up spending two hours troubleshooting, two times.

I've used NFS with FreeNAS before, but since I built out an internal DNS infrastructure I had an issue. I could not mount the NFS shares from ESXi. When I removed the DNS configuration from FreeNAS, the shares mount. The ESXi hostnames can be resolved from the DNS server that was configured in FreeNAS, but the shares would not mount at all. No ACL for networks, hosts, permissions correct. The only change to resolve this was to remove the DNS server configured in FreeNAS.

Any thoughts as to why this could be?
 
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My bet is it is a problem with reverse lookup. You say the host names can be resolved, but can the IP's be reverse looked up? Below is the forward lookup.
Code:
<elliot@alfred:/usr/home/elliot> nslookup alfred
Server:		 127.0.0.1
Address:		127.0.0.1#53

Name:   alfred.oau.org
Address: 192.168.XXX.8


What FreeNAS (and almost any other host, particularly *nix ones) is likely doing is this.
Code:
<elliot@alfred:/usr/home/elliot> nslookup 192.168.XXX.8
8.XXX.168.192.in-addr.arpa	  name = alfred.oau.org.


It is a quirk of *nix systems that have DNS enabled that there is a HUGE pause if a host connects to them, and the source IP cannot be resolved by DNS. You can test this by enabling SSH or (shudder) telnet. Telnet to the box (or telnet to port 22 if you enable SSH) from the ESXi host. If you get a connect and then nothing, just wait 10-30 seconds. If you eventually get the herald/banner from the appropriate service and things work normally, that is the smoking gun of failing reverse lookup. On the off chance that is isn't obvious, I substituted XXX for the actual 3rd octet of my network segment. :smile:
 

Daniel-A

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That's probably it. I don't have reverse lookup zone configured on my DNS. Thanks!
 

jgreco

Resident Grinch
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A side note: it isn't a good idea to use DHCP, DNS, etc., when doing NFS mounts from an ESXi host, at least if you want it to be reliable. Wire things down and refer to them by IP address. I realize that this isn't exactly your problem, but it is often the *next* lesson you might learn the hard way.
 

Daniel-A

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Tracking. I know better than to build a dependency on dns for storage. There are other reasons I would want dns to work such as dynamic replication targets but it will suffice without.
 

jgreco

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And have the DNS system disks running on the storage that depends on it!

Oh PLEASE. What you really need is to set up a virtual FreeNAS instance, create a new thin-provisioned datastore on it, mount that datastore on ESXi, and then run Storage vMotion to move the virtual FreeNAS instance to that datastore. Don't you just love complexity and recursion?
 

Daniel-A

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I really do. Except the virtual FreeNAS boots off an iscsi drive hooked through IPXE that is a raid0 VHD disks with one side in AWS and the other side in Azure over VPN. Then I migrate the DHCP server to the FreeNAS.

giphy.gif
 
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