<div dir="ltr">Dan,<div><br></div><div>So to clarify:</div><div><ul><li>You have two linux Virtual Machines running under a Windows Host server.</li><li>One of the VMs is working normally and experiencing no network problems.</li><li>The other VM is working normally for a short while and then randomly is no longer responding to attempts to connect to the web server service via either its WAN or LAN address. While at the same time the problem is occurring, it <u>is</u> able to establish a successful <u>outbound</u> connection to a device on the internet or your local LAN.</li></ul><div>Do I have that correct?</div></div><div><br></div><div>You've indicated that you can't connect to the web server service running on your Ubuntu 20.04 VM (when it's acting up). You've also said that you can ping your local DNS server from the Ubuntu server. But is the Ubuntu server <u>responding</u> to ping requests while it's misbehaving? If it's still responding to pings even while you can't connect to the web server (apache?) service, then you should maybe focus your efforts on just the web server service. If that's the case, then while you're experiencing the problem, stop/restart apache (or whatever web server you're using) and see if just doing that alone is enough to get it working again, at least temporarily. If solely restarting apache (or whatever) makes it work for a little while, then focus there. If that makes no difference, then at least you can exclude that from your consideration.</div><div><br></div><div>If the Ubuntu server <u>isn't</u> responding to pings (assuming you're not specifically blocking ICMP Echo Requests in the local Ubuntu firewall, if it's enabled) or on other ports like maybe SSH when it normally DOES respond to those services, then you're looking at a more core problem in your Ubuntu VM or perhaps a network issue outside of your VM entirely...maybe at the host Windows Server or elsewhere.</div><div><br></div><div>Based on the little bit of info you've provided so far, my <u>blind</u> <u>guess</u> is that your network is fine; your host Windows Server is fine; your Ubuntu server VM is fine; and that you may have a problem in your web server service running on the problem Ubuntu server VM. But it's just a complete guess at this point. Just keep trying to cut the problem in half until you arrive at a plausible root cause. For example:</div><div><ul><li>Is it hardware or software? Well, your Windows Server is fine and one of the two Ubuntu VMs is fine, so the server hardware is probably fine.</li><li>So software then: Is it your host Windows Server/virtualization hypervisor software or is it something within the VM's operating system? Well, the other Ubuntu VM works fine and so does the host Windows Server, so it's probably just within the problematic Ubuntu VM.</li><li>So just one Ubuntu server then: Does ALL inbound and outbound network communication stop? No...just inbound. Ok. So it's probably not a general network interface problem or an IP address conflict.</li><li>So network interface works, but something's blocking inbound network traffic: What's good at blocking inbound network traffic? The firewall. Is it Ubuntu's firewall? Disable it, if it's safe to do so.</li><li>Problem still exists with the Ubuntu firewall disabled? Then not the Ubuntu firewall. Maybe a firewall on the Windows Server host is misconfigured in some way? Do all services running on the Ubuntu server stop responding or just the web server?</li><li>Can still ping the Ubuntu server even while you can't connect to the HTTP(S) server? Can you SSH into the Ubuntu server? Yes; yes?...Probably something to do with just the HTTP(S) server.</li><li>Can't ping the Ubuntu server AND can't connect via HTTP(s) to the web server service AND can't connect via SSH...AND the ubuntu server firewall is disabled...but can still establish outbound connections...either something's wrong in the Ubuntu server core OS or something that has an overarching ability to block incoming network traffic to the Ubuntu VM is at play...The host Windows Server's firewall? Network routing problem?</li></ul></div><div>Until you can methodically narrow down the problem and define it a little bit, it could really be just about anything. The trick is to just keep cutting the (any) problem down into logical halves until you've reached a small enough half that you can deal with. </div><div><br></div><div>HTH and good luck!</div><div>Chad</div><div><div><div dir="ltr" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div>______________________________<br><b>Chad Neeper</b><br><font size="1">Senior Systems Engineer</font><br><br><b>Level 9 Networks</b><br><font size="1">740-548-8070 (voice)<br>866-214-6607 (fax)</font><br><br><font size="1"><i>Full IT/Computer consulting services -- Specialized in public libraries</i></font><br></div></div></div></div></div></div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Mar 17, 2022 at 12:42 PM Danny Will via OPLINTECH <<a href="mailto:oplintech@lists.oplin.org" target="_blank">oplintech@lists.oplin.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi all,<br>
It's not often that I'm stumped but...<br>
<br>
I have a windows 2019 server with 2 virtual machines running Ubuntu Linux server (no GUI installed). Both are 20.0.4.3 but, that really isn't the important part. Both are running websites. One is a copy of the Meeting Room Booking System and it runs perfect. The other is a slightly modified copy of Omeka database system that we use as our local history site. Cataloging newspapers, High School yearbooks, Photographs, & just about anything else that is historically worthy of keeping. While it is getting kind of large, it works fine EXCEPT...<br>
<br>
>From time to time, & without any indication of why, this site cannot be reached. I have tried the WAN address by both FQDN & IP address. I have tried the LAN address (10.66.76.24) to no avail. If I log onto the virtual machine, I can ping the internal DNS server & any external address (<a href="http://google.com" rel="noreferrer" target="_blank">google.com</a>, etc.).<br>
This comes and goes without rhyme or reason. At this point I am ready to pull out what little hair I have out.<br>
<br>
I thought at 1st, that the firewall was the issue, so I changed things around to by-pass the usual firewall. Worked for a little while then it was down again (worked for maybe 2 or 3 hours, just enough time that I left for home just to hear a short time later we were getting calls about it being down again). So it was not the firewall. I made a small change to the NIC settings on the server. It worked fine after that...for 20 minutes back down.<br>
<br>
TIA<br>
<br>
Dan Will<br>
Meigs County District Public Library<br>
Technology Supervisor<br>
<a href="mailto:danwill@meigslibrary.org" target="_blank">danwill@meigslibrary.org</a><mailto:<a href="mailto:danwill@meigslibrary.org" target="_blank">danwill@meigslibrary.org</a>><br>
740.992.5813<br>
<br>
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