Connection and disconnection loop on login
I'm using manjaro and with the latest version of all packet (NM is at 1.20.0) when i login the ethernet network keep disconnecting and reconnecting every few seconds until i manually disconnect it and then i can connect to it without problems. After some trubleshooting it seems that the cause is the speed negotiation: it work fine only if i set it manually to 100 Mbit.
The problem is already present in NetworkManager 1.18.2 but if i downgrade to 1.18.0 everything work fine.
An extract of the log where you can see the repeated connection and disconnection:
ago 22 08:39:18 manjaro-pc NetworkManager[1197]: <info> [1566455958.1573] device (enp5s0): state change: activated -> unavailable (reason 'carrier-changed', sys-iface-state: 'managed')
ago 22 08:39:18 manjaro-pc NetworkManager[1197]: <info> [1566455958.1662] manager: NetworkManager state is now CONNECTED_LOCAL
ago 22 08:39:19 manjaro-pc NetworkManager[1197]: <info> [1566455959.5016] agent-manager: req[0x55a50c52b840, :1.65/org.kde.plasma.networkmanagement/1000]: agent registered
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.0495] device (enp5s0): carrier: link connected
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.0497] device (enp5s0): state change: unavailable -> disconnected (reason 'carrier-changed', sys-iface-state: 'managed')
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.0507] policy: auto-activating connection 'Connessione via cavo 1' (40772538-e981-3fb2-9c85-08aeba3e2089)
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.0511] device (enp5s0): Activation: starting connection 'Connessione via cavo 1' (40772538-e981-3fb2-9c85-08aeba3e2089)
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.0512] device (enp5s0): state change: disconnected -> prepare (reason 'none', sys-iface-state: 'managed')
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.0516] manager: NetworkManager state is now CONNECTING
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.0963] device (enp5s0): state change: prepare -> config (reason 'none', sys-iface-state: 'managed')
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.0972] device (enp5s0): state change: config -> ip-config (reason 'none', sys-iface-state: 'managed')
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <warn> [1566455961.0987] acd[0x55a50c511450,2]: couldn't init ACD for announcing addresses on interface 'enp5s0': Operazione non permessa
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.0989] device (enp5s0): state change: ip-config -> ip-check (reason 'none', sys-iface-state: 'managed')
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.1019] device (enp5s0): state change: ip-check -> secondaries (reason 'none', sys-iface-state: 'managed')
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.1022] device (enp5s0): state change: secondaries -> activated (reason 'none', sys-iface-state: 'managed')
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.1025] manager: NetworkManager state is now CONNECTED_LOCAL
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.1032] manager: NetworkManager state is now CONNECTED_SITE
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.1033] policy: set 'Connessione via cavo 1' (enp5s0) as default for IPv4 routing and DNS
ago 22 08:39:21 manjaro-pc NetworkManager[1197]: <info> [1566455961.1087] device (enp5s0): Activation: successful, device activated.
ago 22 08:39:27 manjaro-pc NetworkManager[1197]: <info> [1566455967.0990] device (enp5s0): state change: activated -> unavailable (reason 'carrier-changed', sys-iface-state: 'managed')
ago 22 08:39:27 manjaro-pc NetworkManager[1197]: <info> [1566455967.1085] manager: NetworkManager state is now CONNECTED_LOCAL
ago 22 08:39:29 manjaro-pc NetworkManager[1197]: <info> [1566455969.8898] device (enp5s0): carrier: link connected
ago 22 08:39:29 manjaro-pc NetworkManager[1197]: <info> [1566455969.8901] device (enp5s0): state change: unavailable -> disconnected (reason 'carrier-changed', sys-iface-state: 'managed')
ago 22 08:39:29 manjaro-pc NetworkManager[1197]: <info> [1566455969.8914] policy: auto-activating connection 'Connessione via cavo 1' (40772538-e981-3fb2-9c85-08aeba3e2089)
ago 22 08:39:29 manjaro-pc NetworkManager[1197]: <info> [1566455969.8923] device (enp5s0): Activation: starting connection 'Connessione via cavo 1' (40772538-e981-3fb2-9c85-08aeba3e2089)
ago 22 08:39:29 manjaro-pc NetworkManager[1197]: <info> [1566455969.8924] device (enp5s0): state change: disconnected -> prepare (reason 'none', sys-iface-state: 'managed')
ago 22 08:39:29 manjaro-pc NetworkManager[1197]: <info> [1566455969.8929] manager: NetworkManager state is now CONNECTING
ago 22 08:39:29 manjaro-pc NetworkManager[1197]: <info> [1566455969.9405] device (enp5s0): state change: prepare -> config (reason 'none', sys-iface-state: 'managed')
ago 22 08:39:29 manjaro-pc NetworkManager[1197]: <info> [1566455969.9416] device (enp5s0): state change: config -> ip-config (reason 'none', sys-iface-state: 'managed')
ago 22 08:39:29 manjaro-pc NetworkManager[1197]: <warn> [1566455969.9438] acd[0x55a50c436c00,2]: couldn't init ACD for announcing addresses on interface 'enp5s0': Operazione non permessa
ago 22 08:39:29 manjaro-pc NetworkManager[1197]: <info> [1566455969.9439] device (enp5s0): state change: ip-config -> ip-check (reason 'none', sys-iface-state: 'managed')
ago 22 08:39:29 manjaro-pc NetworkManager[1197]: <info> [1566455969.9580] device (enp5s0): state change: ip-check -> secondaries (reason 'none', sys-iface-state: 'managed')
ago 22 08:39:29 manjaro-pc NetworkManager[1197]: <info> [1566455969.9583] device (enp5s0): state change: secondaries -> activated (reason 'none', sys-iface-state: 'managed')
The reason for the disconnections seems to be "carrier-changed"