I just upgraded from 16.04 to 18.04 on my main desktop machine. I've got an r8168 network card. I got gigabit speeds in 16.04 and now am now only getting 100Mbps in 18.04. I've tried both the r8169 and r8168-dkms drivers. After doing the upgrade, I've swapped network cables and switches to ensure this isn't a hardware problem.
The NIC is the on-board NIC for an MSI x370 Gaming Plus motherboard.
Unfortunately, I don't have this debug information from 16.04; the below is from after the upgrade to 18.04.
$ sudo lshw -C network *-network description: Ethernet interface product: RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller vendor: Realtek Semiconductor Co., Ltd. physical id: 0 bus info: pci@0000:1e:00.0 logical name: eth0 version: 15 serial: 30:9c:23:0c:9a:94 size: 100Mbit/s capacity: 1Gbit/s width: 64 bits clock: 33MHz capabilities: pm msi pciexpress msix bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation configuration: autonegotiation=on broadcast=yes driver=r8168 driverversion=8.045.08-NAPI duplex=full ip=192.168.1.2 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s resources: irq:46 ioport:f000(size=256) memory:fd604000-fd604fff memory:fd600000-fd603fff $ sudo ethtool eth0 Settings for eth0: Supported ports: [ TP ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Supported pause frame use: No Supports auto-negotiation: Yes Supported FEC modes: Not reported Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Advertised pause frame use: No Advertised auto-negotiation: Yes Advertised FEC modes: Not reported Speed: 100Mb/s Duplex: Full Port: Twisted Pair PHYAD: 0 Transceiver: internal Auto-negotiation: on MDI-X: Unknown Supports Wake-on: pumbg Wake-on: g Current message level: 0x00000033 (51) drv probe ifdown ifup Link detected: yes $ lsmod | grep r816 r8168 524288 0 $ dmesg | egrep '(eth0)|(r816)' [ 1.036881] r8168: loading out-of-tree module taints kernel. [ 1.037195] r8168: module verification failed: signature and/or required key missing - tainting kernel [ 1.037822] r8168 Gigabit Ethernet driver 8.045.08-NAPI loaded [ 1.052489] r8168: This product is covered by one or more of the following patents: US6,570,884, US6,115,776, and US6,327,625. [ 1.052496] r8168 Copyright (C) 2017 Realtek NIC software team <email@example.com> [ 42.034465] eth0: 0xffffa7790007d000, 30:9c:23:0c:9a:94, IRQ 46 [ 42.087610] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready [ 47.210737] r8168: eth0: link up [ 47.210752] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready # note: did ethtool -r eth0 here [ 180.421766] r8168: eth0: link down [ 185.588203] r8168: eth0: link up