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After upgrade to Ubuntu 18.04 I get a question mark instead of wifi icon, and I cannot visit some websites - these websites change sometimes but a website I recently been having problem loading is edx.org. Both problems go away as I connect to a VPN server with openconnect.

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  • My Speed was slow too when I first upgraded to 18.04 so I changed the MTU to match my connection (Ended up being 1496). Try this fix. Oct 2, 2018 at 9:23

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Click on Network Setiings...Upper right... enter image description here

Then open Identity.... enter image description here

Strategy and Test....

STRATEGY

The strategy is simple... Ping a series of diffent sizes, and this will help narrow down the MTU size. A ping is 28 bytes on it's own. A typical LAN connection has an MTU of 1500 bytes. So we need to remember to subtract 28 from the MTU we really want to test. For example, if we want to test an MTU of 1500, first ping and set the size to 1473, this should fail as we are sending a ping that is 1501 bytes in size, with the Do Not Fragment option set. you should get an output similar to the following:

jon@JonM-LabPC:/$ ping -c 2 -M do 8.8.8.8 -s 1473 PING 8.8.8.8 (8.8.8.8) 1473(1501) bytes of data. ping: local error: Message too long, mtu=1500 ping: local error: Message too long, mtu=1500

--- 8.8.8.8 ping statistics --- 2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 1006ms

We can see the error "Message too long", followed by the actual MTU size. Please be aware that not all Linux distros will have this same output... For Checkpoint's Gaia, you will get something similar to this:

[Expert@R7730StandAlone:0]# ping -c 2 -M do -s 1473 8.8.8.8 PING 8.8.8.8 (8.8.8.8) 1473(1501) bytes of data. From 172.26.176.150 icmp_seq=1 Frag needed and DF set (mtu = 1500) From 172.26.176.150 icmp_seq=1 Frag needed and DF set (mtu = 1500)

--- 8.8.8.8 ping statistics --- 0 packets transmitted, 0 received, +2 errors

So, depending on the output you get, you can further validate that the MTU is 1500 by sending a ping that is exactly 1500 bytes in size, rather than 1501. You would just set the size to 1472. This will be the MTU for 99% of internal LAN connections, and most residential cable modems.

Just Keep going up till correct MTU is found....

steve@steve:~$ ping -c 2 -M do 8.8.8.8 -s 1468
PING 8.8.8.8 (8.8.8.8) 1468(1496) bytes of data.
1476 bytes from 8.8.8.8: icmp_seq=1 ttl=118 time=26.3 ms
1476 bytes from 8.8.8.8: icmp_seq=2 ttl=118 time=26.7 ms

--- 8.8.8.8 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 26.311/26.525/26.739/0.214 ms

steve@steve:~$ ping -c 2 -M do 8.8.8.8 -s 1469
PING 8.8.8.8 (8.8.8.8) 1469(1497) bytes of data.
ping: local error: Message too long, mtu=1496
ping: local error: Message too long, mtu=1496

--- 8.8.8.8 ping statistics ---
2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 
1029ms

PING 8.8.8.8 (8.8.8.8) 1468 (1496) bytes of data.

When this message is received, you have determined MTU....

ping: local error: Message too long, mtu=1496
ping: local error: Message too long, mtu=1496
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