ESXi Hosts disconnected from vCenter Linux Appliance

Running the VMware Linux appliance on 1 of 3 ESXi 5.1 hosts.  All 3 ESXi host are shown as disconnected and I cannot reconnect them.  

Right-clicking the host and choosing 'Connect' first gives me a "Authenticity of the host's SSL certificate is not verified" warning.  After closing that dialog box, I get to the "Specify Connection Settings" where I enter the ESXi hostname (pre-populated) and the username/password.  I receive a popup stating "Unable to verify the authenticity of the specified host.  I choose "Yes" to continue.I then receive the following error:

"Cannot contact the specified host. The host may not be available on the network, a network configuration problem may exist or the management services on this host many not be responding."

I get the same error trying to connect to each of the 3 ESXi servers.  Also noteworthy is that if I SSH into the vCenter Linux appliance and run a ping test, I get dropped pings.  "IFCONFIG" shows a lot of dropped packets.  If I SSH directly into the ESXi host where the vCenter Linux appliance is running and do a ping test, there is no packet loss.

From the CLI of the vCenter Linux Appliance I can successfully ping the ESXi hosts via the FQDN, but there is packet loss.

Any ideas on how to get the ESXi hosts reconnected?  The vCenter Linux appliance gets it's IP address from DHCP so that would have to be taken into account if a reboot of the VM is suggested.  I cannot do anything that would interrupt the running VMs on any of the hosts.

Thanks in advance for your ideas/assistance!
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
If you are having network issues, between vCenter Server and Host ESXi server, I would investigate and look at your networking?

Also you are using vCenter Server 5.1 and above for your ESXi 5.1 servers ?
I ran into this when I had a name collision between some existing ESXi hosts and new hosts that were being deployed.

Check to see if you have an IP address conflict on the management IPs of your ESXi hosts.

Also, check if there's an IP address conflict with the vCenter server somewhere.

None of this should affect the guests; vCenter is only used for managing the ESXi hosts.  You can also restart the management agents on the hosts without affecting the guests.
CipherUserAuthor Commented:
I think I found the problem.  The vCenter Linux appliance has a DHCP assigned DNS server that is handing out bogus information.  Is there a way to manually change the DNS server being used? Maybe via SSH?  If not, I can try a reboot of the linux vCenter appliance.  Will this affect any running VMs? I don't think it should but wanted to double-check.

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You can reboot and change network settings of your vCenter at will with no effect on guests.  

In my opinion, your two best choices are either a static IP or fixing the DHCP issue.  If the DHCP issues a different DNS server from what you want to use, just set a static IP on the vCenter.
I just checked, and I can SSH to my vCenter appliance.

Looks like you would edit the /etc/resolv.conf file.

A quick check shows that the vi and vim editors are on the image, but nano is not.  Are you familiar with these editors?

command to edit the file:  vi /etc/resolv.conf

type i to insert
enter lines similar to:
nameserver w.x.y.z
nameserver l.m.n.o

Hit escape when you're done editing.  Then type colon w q (":wq") and hit enter.  (Colon for commands, w for write, q for quit.)

You will need to either restart the network or reboot for the change to be effective.  I would suggest a reboot, unless you're familiar with Linux.  (Just type "reboot" at the command line.)

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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Your best attack, would be to check your DNS server, and fix it!

otherwise DNS information will be replicated between DNS servers, and causing issues elsewhere!

As I said, VMware vSphere is only as good as your networking, if your networking e.g. DHCP, DNS, WINS, is incorrect, you will have a world off issues.
Alternately, you can edit the /etc/hosts file just like you would the hosts file for Windows.
CipherUserAuthor Commented:
The DNS and DHCP servers are handled by another group.  I have no access to getting those changes made.  Editing the resolv.conf file fixed the problem immediately with no restart of any services needed.  Granted it's a bit of a workaround, but it fixed my problem.

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