[Solved] Ping - yes, Tracepath - yes, why doesn't it resolve server addresses?

Question

Drivers

UPD: Solved. It's not about the reel, and not even about the cab. Business in provider and the 80th port.
Good afternoon!
Something went wrong and for no reason apt-get on the hypervisor stopped resolving server addresses.
On virtual machines that are spinning on this machine - everything is fine.
If you contact the host, for example, security.ubuntu.com, for example, via ping, then it will be:

[email protected]:/etc/apt/apt.conf.d$ ping security.ubuntu.com
PING security.ubuntu.com (91.189.91.15) 56(84) bytes of data.
64 bytes from likho.canonical.com (91.189.91.15): icmp_seq=1 ttl=50 time=138 ms

Tracepath:

[email protected]:/etc/apt/apt.conf.d$ tracepath security.ubuntu.com
1?: [LOCALHOST] pmtu 1500
1: 192.168.1.100 0.677ms
1: 192.168.1.100 0.440ms
2: 31-132-161 -65.bks-tv.ru 1.910ms asymm 36
3: 10.128.155.1 2555.083ms asymm 37
4: 172.31.255.34 1.064ms
5: bnk01.transtelecom.net 14.717ms asymm 11 8: be2397.ccr22.stocogentco.at .com 57.057ms asymm 13 9: be2282.ccr42.ham01.atlas.cogentco.com 66.558ms asymm 12
6:
149.6.168.202 be4027.ccr21.sto01.atlas.cogentco.com 68.837ms asymm 14
10: be2187.ccr42.ams03.atlas.cogentco.com 60.319ms asymm 12
11: be2183.ccr22.lpl01.atlas.cogentco.com 66.983ms asymm 13
3: 10.128.155.1 2167.897ms asymm 37
12: be2387.ccr22.bos01.atlas.cogentco.com 136.917ms asymm 14 33.218
:3 ms asymm 14
14: orobas.canonical.com 132.985ms reached
Resume: pmtu 1500 hops 14 back 15

But through apt-get it will be just like this:

[email protected]:/etc/apt/apt.conf.d$ sudo apt-get update
err security.ubuntu.com trusty-security InRelease

As a result, I can neither update nor install any software. Reinstalling the system is not possible at all.
What and where to look to get apt working again?
UPD:
Further, it was found out that also wget with curl does not resolve hosts by name. Other machines on the network accessing the internet through the same router work just fine. Proxies are not.

Answer 1

The problem is not in apt, but in the fact that your DNS resolution has fallen off. Check /etc/resolv.conf (or wherever the DNS servers are registered on Linux) and then check the availability of the DNS servers specified in this file. You can make nslookpu ya.ru and then post the result of the execution here for further diagnostics, along with the contents of resolv.conf.