"Activation of network connection failed" for wired connection, even though it works in interim (18.04)

Question

I am connecting an external device via ethernet. In network manager, it shows the wired connection as "Connecting". I am able to ping and SSH to the remote device during this phase, the connection works fine.

After a period of time (~30s?) I get a message "Activation of network connection failed" and the wired connection is disabled. I have to re-enable it (or unplug/plug in the cable) to continue working.

Potentially relevant information:

• I have a stable wifi connection to the internet, but the problem also repros when I disable it.
• The remote device does not have internet connectivity.
• The remote device is ipv6 only.
• I'm running a Dell XPS13 and using a USB-C to ethernet adapter.
• I have observed the behaviour on duplicates of all external hardware (cables, devices).
• A co-worker is using archlinux and doesn't have this problem.

Logs:

# Excerpt from: journalctl -u NetworkManager
Aug 17 17:59:47 yoshi NetworkManager[1043]: <info>  [1534553987.5996] device (enx00e04c00072b): Activation: starting connection 'Wired connection 1' (74876abf-ba83-38b1-813d-1fa271132731)
Aug 17 17:59:47 yoshi NetworkManager[1043]: <info>  [1534553987.6002] device (enx00e04c00072b): state change: disconnected -> prepare (reason 'none', sys-iface-state: 'managed')
Aug 17 17:59:47 yoshi NetworkManager[1043]: <info>  [1534553987.6012] device (enx00e04c00072b): state change: prepare -> config (reason 'none', sys-iface-state: 'managed')
Aug 17 17:59:47 yoshi NetworkManager[1043]: <info>  [1534553987.6026] device (enx00e04c00072b): state change: config -> ip-config (reason 'none', sys-iface-state: 'managed')
Aug 17 18:00:19 yoshi NetworkManager[1043]: <info>  [1534554019.5847] device (enx00e04c00072b): state change: ip-config -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed')
Aug 17 18:00:19 yoshi NetworkManager[1043]: <warn>  [1534554019.5858] device (enx00e04c00072b): Activation: failed for connection 'Wired connection 1'
Aug 17 18:00:19 yoshi NetworkManager[1043]: <info>  [1534554019.5870] device (enx00e04c00072b): state change: failed -> disconnected (reason 'none', sys-iface-state: 'managed')

Questions:

1. What is Ubuntu using to determine that this connection failed, given that ping/ssh work fine?
2. How can I fix it?

Update: I changed the settings for the connection so that IPv4 was disabled and IPv6 was Link-Local Only (from "Automatic"). This appears to have fixed the issue, but I don't really understand what I've done so an answer with more details (and confirmation that this is a legitimate fix) would be appreciated.

Answer 1

IP addresses don't appear automagically: they need a DHCP server to work reliably under all circumstances.

The IPV6 protocol allows for SLAAC to assign a temporary IP address, but the real solution is to install a DHCP server on your machine and your colleague running Arch probably has one running.

As to your questions: 1 and 2 are interconnected "Link-Local only" forces SLAAC to be used and to bypass the DHCP server even if there would be one.