Ubuntu 17.10 shows my gigabit ethernet connection at 100Mbps

Question

I have just installed Ubuntu 17.10 on my Toshiba Satellite L50t-a-140 laptop which has a gigabit ethernet wired adapter connected to a gigabit ethernet switch, but Ubuntu reports the link speed at 100Mbps. How can I work out why it is not reporting a gigabit ethernet connection?

~$ sudo lshw -C network
  *-network                 
       description: Ethernet interface
       product: AR8161 Gigabit Ethernet
       vendor: Qualcomm Atheros
       physical id: 0
       bus info: pci@0000:01:00.0
       logical name: enp1s0
       version: 10
       serial: 00:8c:fa:94:4f:09
       size: 100Mbit/s
       capacity: 1Gbit/s
       width: 64 bits
       clock: 33MHz
       capabilities: pm pciexpress msi msix bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=alx duplex=full ip=192.168.1.4 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s
       resources: irq:16 memory:b0500000-b053ffff ioport:3000(size=128)
  *-network DISABLED
       description: Wireless interface
       product: QCA9565 / AR9565 Wireless Network Adapter
       vendor: Qualcomm Atheros
       physical id: 0
       bus info: pci@0000:02:00.0
       logical name: wlp2s0
       version: 01
       serial: 28:e3:47:02:df:c2
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress bus_master cap_list rom ethernet physical wireless
       configuration: broadcast=yes driver=ath9k driverversion=4.13.0-38-generic firmware=N/A latency=0 link=no multicast=yes wireless=IEEE 802.11
       resources: irq:17 memory:b0400000-b047ffff memory:b0480000-b048ffff

Solution

My guess is a bad or poor-quality ethernet cable. Has that computer ever worked at Gbit? Have you tried any live CD's? Have you tried that ethernet cable on a machine that you know works at full speed? From the looks of it, it looks like a hardware issue.

I've never used lshw to determine speed, but you might want to try typing cat /sys/class/net/enp1s0/speed and see what it says there.

Comments

[WinEunuuchs2Unix]

These values are sometimes inaccurately reported. Run a speed test to find out for sure.

[Boris Hamanov]

Change your ethernet cable to cat5 or better, and/or check to make sure that it's connected to a gigabit port on your switch/router.

[3guesses]

OK, so it could possibly be the cable. I have tested this set-up with 2 cables, neither is especially old and using either of them with my old Sony VGN-FW51MF (running Windows XP!) reports a link speed of 1.0Gbps. I'm wondering if it could be the Ubuntu driver for my NIC. This is the first time I have tried connecting this laptop to my gigabit switch so I don't know if it will connect at gigabit speeds but I can see no reason why it shouldn't. What software should I use to test the actual connection speed?

[Organic Marble]

A cable swap fixed this for me when I noticed it long ago. Definitely the first thing to try.

[Thomas Ward]

This doesn't really provide a true answer in its current form to the OP's actual question... this is more along the lines of a good comment though.

[Brian S.]

It won't let me leave a comment, because I don't have a "reputation" yet. So I left answer instead.

[3guesses]

OK, so I tried using Slax, Puppy Linux and Fedora live CDs and they all showed 100Mbps.

[3guesses]

ethtool enp1s0 showed supported and advertised speeds which included 1000baseT. I tried ethtool -s enp1s0 speed 1000 but I just got "Invalid argument/not setting speed". Same for 100 and 10. Then I did ethtool -s enp1s0 autoneg off and I could set the speed to either 10 or 100 but still not 1000. However I now can't set autonegotiation back on! I get "Invalid argument/not setting autoneg". Any suggestions?

[3guesses]

A reboot has switched autonegotiation back on! Phew...

[Brian S.]

I have heard that some cards, for some reason, don't report their speed correctly to the OS (Does it show on the router the connections speed?). As far NIC drivers go, either they don't work at all, or they just work kinda crappy. I've never seen speed negotiation problems. I've never seen a default setting not work. 99.99% of the time with this issue it is the cable, a setting on the router, or somebody not having enough ports on their router and they add a switch not realizing their switch is a 10/100). Keep us posted if you figure it out.