[OPLINTECH] Intermittent network issues

Sat Mar 19 17:55:46 EDT 2022

Dan,

So to clarify:

   - You have two linux Virtual Machines running under a Windows Host
   server.
   - One of the VMs is working normally and experiencing no network
   problems.
   - 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 *is* able to establish a successful *outbound* connection
   to a device on the internet or your local LAN.

Do I have that correct?

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 *responding* 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.

If the Ubuntu server *isn't* 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.

Based on the little bit of info you've provided so far, my *blind* *guess*
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:

   - 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.
   - 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.
   - 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.
   - 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.
   - 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?
   - 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.
   - 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?

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.

HTH and good luck!
Chad
______________________________
*Chad Neeper*
Senior Systems Engineer

*Level 9 Networks*
740-548-8070 (voice)
866-214-6607 (fax)

*Full IT/Computer consulting services -- Specialized in public libraries*

On Thu, Mar 17, 2022 at 12:42 PM Danny Will via OPLINTECH <
oplintech at lists.oplin.org> wrote:

> Hi all,
>      It's not often that I'm stumped but...
>
> 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...
>
> 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 (
> google.com, etc.).
> This comes and goes without rhyme or reason. At this point I am ready to
> pull out what little hair I have out.
>
> 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.
>
> TIA
>
> Dan Will
> Meigs County District Public Library
> Technology Supervisor
> danwill at meigslibrary.org<mailto:danwill at meigslibrary.org>
> 740.992.5813
>
> _______________________________________________
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> OPLINTECH at lists.oplin.org
> http://lists.oplin.org/mailman/listinfo/oplintech
>
> ****** ****** Ready to level up your library's website to something that
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