Ubuntu 18.04. Sudden DSL connection degrading - on and off - inconsistent slow connection to websites

Question

I have been using my rig with no problems for 2 years. Nothing change in the last days in terms of ISP etc... Suddenly I am experiencing troubles with my internet connection. Often I go to my favorite sites like Amazon or Wal Mart for online shopping and the page does not resolve DNS issues. etc... Youtube videos take forever to load. Or have a black screen and then suddenly starts.

Basically what used to be a solid and consistent internet connection is close to almost useless.

$ ls -al /var/crash
total 94492
drwxrwsrwt  2 root     whoopsie     4096 Oct  9 20:58 .
drwxr-xr-x 15 root     root         4096 Dec 16  2020 ..
-rw-r-----  1 user  whoopsie 93889664 Oct  9 20:50 _opt_google_chrome_chrome.1000.crash
-rw-r--r--  1 user  whoopsie        0 Oct  9 20:50 _opt_google_chrome_chrome.1000.upload
-rw-------  1 whoopsie whoopsie        0 Oct  9 20:58 _opt_google_chrome_chrome.1000.uploaded
-rw-r-----  1 user  whoopsie  2852391 Oct  2 22:55 _usr_bin_file-roller.1000.crash
-rw-r--r--  1 user  whoopsie        0 Oct  2 22:55 _usr_bin_file-roller.1000.upload
-rw-------  1 whoopsie whoopsie        0 Oct  3 10:42 _usr_bin_file-roller.1000.uploaded


$ free -h
              total        used        free      shared  buff/cache   available
Mem:           7.7G        1.4G        4.2G        134M        2.2G        5.9G
Swap:          4.0G          0B        4.0G

Any help is greatly appreciated as I remain a very basic user of linux.

PS: BTW other computers and smart televisions and phones at my house are not experiencing any internet connection issues at all either Wi_fi or DSL.

PS: When I went to restart I now see a black screen that says "Failed to start Network manager".

$ tracepath www.amazon.com 1?: [LOCALHOST] pmtu 1500 1: modem.Home 4.305ms 1: no reply 2: modem.Home 72.534ms pmtu 1492 2: tukw-dsl-gw68.tukw.qwest.net 53.848ms 3: tukw-agw1.inet.qwest.net 24.760ms 4: 99.82.182.74 24.713ms asymm 5 5: 52.95.55.223 25.652ms asymm 8 6: 150.222.237.55 24.320ms asymm

    $ sudo lshw -C network
      *-network                 
           description: Ethernet interface
           product: Ethernet Connection I217-LM
           vendor: Intel Corporation
           physical id: 19
           bus info: pci@0000:00:19.0
           logical name: eno1
           version: 04
           serial: c8:1f:66:ac:5b:36
           size: 1Gbit/s
           capacity: 1Gbit/s
           width: 32 bits
           clock: 33MHz
           capabilities: pm msi bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
           configuration: autonegotiation=on broadcast=yes driver=e1000e driverversion=3.2.6-k duplex=full firmware=0.13-4 ip=192.168.0.14 latency=0 link=yes multicast=yes port=twisted pair speed=1Gbit/s
           resources: irq:31 memory:f7d00000-f7d1ffff memory:f7d3d000-f7d3dfff ioport:f080(size=32)
      *-network DISABLED
           description: Wireless interface
           physical id: 1
           bus info: usb@3:1
           logical name: wlx1cbdb9dfc01d
           serial: 1c:bd:b9:df:c0:1d
           capabilities: ethernet physical wireless
           configuration: broadcast=yes driver=r8712u multicast=yes wireless=unassociated

$  cat /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback
mtu 1450

$ cat /etc/netplan/*.yaml
# Let NetworkManager manage all devices on this system
network:
  version: 2
  renderer: NetworkManager

Answer 1

Change /etc/network/interfaces...

From:

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback
mtu 1450

To this:

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

Change your Wired Connection profile...

Because of DSL, change MTU from automatic, 1500, or whatever it is, to 1492.

Reboot and retest.

Update #1:

Note: I placed this here just in case it's required to manually determine that 1492 is the correct setting. First reset MTU to 1500, reboot, and then follow the instructions.

Your problem is with the MTU setting for your DSL connection.

There's a MTU setting in Ubuntu's network configuration, and a WAN MTU setting in your router.

For DSL, a common MTU setting is 1492. Just go ahead and try this value first and see if your web sites are now accessible.

To determine the correct setting, start with all MTU settings = 1500 and VPN = off. (VPN requires different testing).

In the terminal:

    ping [-c count] [-M do] [-s packet_size] [host]

The options used are:

• c count: number of times to ping
• M hint: Select Path MTU Discovery strategy. may be either do (prohibit fragmentation, even local one), want (do PMTU discovery, fragment locally when packet size is large), or dont (do not set DF flag).
• s packet_size: Specifies the number of data bytes to be sent.

You should always start at 1472 and work your way down by 10 each time. Once you get a reply, go up by 1 until you get a fragmented packet. Take that value (last good value) and add 28 to the value to account for the various TCP/IP headers. Eg. let's say that 1452 was the proper packet size (where you first got an ICMP reply to your ping). The actual MTU size would be 1480, which is the optimum for the network we're working with.

    ping -c 4 -M do -s 1472 8.8.8.8 # this will probably show fragmentation

    ping -c 4 -M do -s 1462 8.8.8.8 # may show fragmentation

    ping -c 4 -M do -s 1452 8.8.8.8 # no fragmentation?

    ping -c 4 -M do -s 1453 8.8.8.8 # still no fragmentation?

reference: How to determine the proper MTU size with ICMP pings