[SOLVED] DNS Suddenly STOPPED! Stretch 9.5 updated regularly

[debiman]

It appears as though /lib/systemd/system/systemd-resolved.service is disabled

it is well possible that name resolution is achieved by different means.
but since you can't ping IPs directly either, this is not crucial atm.
i didn't think this through, just went by thread title...

i could throw in a few wild guesses, but i will wait what HoaS' line of enquiry brings up.

[kevinthefixer]

Not to interrupt the gurus, but the first thing I'd try is rebooting the hardware, all of it, with special attention given to the router if present. Amazing how often something that simple fixes major problems.

As an aside, I once had a user on an Android forum explain that he didn't think he had to go to "all the trouble" because he didn't think there was anything wrong with his router. After he'd asked for advice! Trouble rebooting a router? I recommend that be done at least monthly just as a routine maintenance item, it takes about 5 minutes, mostly waiting 2-3 minutes to be sure the RAM is voided!

[w4kh]

Code: Select all

default via 192.168.1.254 dev eth0 onlink

Is that correct? Is your gateway at that address?

Yes. That is the correct Gateway address

Does the ethernet card work if you load up a Debian "live" image?

I am able to ping around the LAN, and connect through the eth0 ethernet card in both directions: that is, I can connect via FileZilla to another machine on the network, and I am connected to the NAS, to iSCSI drives, and, as well, other systems on the LAN can connect and move files to and from the Linux machine.
DNS isn't working

[Head_on_a_Stick]

Have you tried setting the gateway as the nameserver (via /etc/resolv.conf)?

What exactly is the nature of your set up: are you using an ISP-supplied router as the gateway device?

EDIT: please also post the output requested by @p.H

[w4kh]

Have you tried setting the gateway as the nameserver (via /etc/resolv.conf)?

Network Manager seems to do that as a matter of course (with other nameserver lines after)

What exactly is the nature of your set up: are you using an ISP-supplied router as the gateway device?

No, I have an ARRIS Cable Modem and Linksys WRT3200ACM router instead...
The router was selected for its feature set, AND that it could be updated with ExpressVPN.

Therein was the problem. Apparently, early in the morning the system went sideways, ExpressVPN dumped its version into iptables.
Once I discovered that, I copied the iptables-save data into a separate file for potential reloading if that were NOT the issue. Then, I retrieved a backup of the previous iptable, reviewed the settings, and loaded it into the active iptable. That solved the problem.

Thank you very much, especially to Head on a Stick, p.H ... fixing iptables, which I had *NOT* changed myself, was the key. I really appreciate the help offered, and especially the new things I learned.

One last thing:

EDIT: please also post the output requested by @p.H

And here it is, with the good iptables...

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traceroute -n 8.8.8.8
traceroute to 8.8.8.8 (8.8.8.8), 30 hops max, 60 byte packets
 1  192.168.1.254  0.288 ms  0.262 ms  0.232 ms
 2  10.167.0.1  55.985 ms  55.998 ms  55.985 ms
 3  147.75.192.244  58.972 ms  58.994 ms  58.955 ms
 4  * * 147.75.98.20  73.530 ms
 5  198.16.4.86  59.829 ms 198.16.4.90  59.841 ms 198.16.4.88  57.163 ms
 6  198.32.160.130  58.749 ms  58.663 ms 206.130.10.41  59.045 ms
 7  108.170.248.65  58.621 ms  62.028 ms 108.170.248.1  63.342 ms
 8  108.170.235.179  61.988 ms 209.85.243.189  60.807 ms 108.170.238.199  59.718 ms
 9  8.8.8.8  59.592 ms  58.999 ms  59.027 ms