Gigabit card only supports 100 Mbps?

2

My Dell Inspiron 17R 5720 running on Ubuntu 16.04 LTS has a gigabit ethernet card, but it is only capable of utilizing 100Mbps.

I tried another laptop that pulls 150 on the same cable, so I'm pretty sure that my computer is the issue.

I ran some commands:

description: Ethernet interface
   product: RTL8101/2/6E PCI Express Fast/Gigabit Ethernet controller
   vendor: Realtek Semiconductor Co., Ltd.
   physical id: 0
   bus info: pci@0000:03:00.0
   logical name: enp3s0
   version: 05
   serial: REDACTED
   size: 100Mbit/s
   capacity: 100Mbit/s
   width: 64 bits
   clock: 33MHz
   capabilities: pm msi pciexpress msix vpd bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd autonegotiation
   configuration: autonegotiation=on broadcast=yes driver=r8169 driverversion=2.3LK-NAPI duplex=full firmware=rtl_nic/rtl8105e-1.fw ip=192.168.1.13 latency=0 link=yes multicast=yes port=MII speed=100Mbit/s
   resources: irq:26 ioport:2000(size=256) memory:f1404000-f1404fff memory:f1400000-f1403fff

Why is it only capable of using 100Mbps when it clearly says Gigabit Ethernet Controller?

B.Cakir

Posted 2018-06-30T21:40:48.017

Reputation: 23

What does it connect to? Both sides have to be able to handle gigabit Ethernet, or else they will downgrade to the fastest common link speed. – ErikF – 2018-06-30T22:54:03.643

@ErikF cat5e cable directly into the carrier modem/router. – B.Cakir – 2018-06-30T23:55:47.250

1If your modem/router is old or doesn't support the latest DOCSIS, etc. the Ethernet port on it (the modem side) may only be a 10/100 and not Gigabit. – LawrenceC – 2018-07-01T03:32:29.003

1What says ethtool enp3s0 (or whatever the interface name is)? – xenoid – 2018-07-01T08:27:40.743

@xenoid "Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full" – B.Cakir – 2018-07-01T09:12:45.293

Please add the full output to the question. But there could be a problem with the Gigabit support even on Windows, see this.

– xenoid – 2018-07-01T11:13:09.730

Answers

2

That's not necessarily a gigabit Ethernet card.

Realtek has both 1G-capable and 100M-only versions of the same product and uses the same PCI VID:PID for both – therefore resulting in the same "product name" under lspci. The only way to distinguish them is by looking at capabilities detected by the driver via ethtool.

(Side note: when checking capabilities via ethtool, ignore the absence of 1G in "Link partner advertised"; the Linux driver appears to actually mask this out if the local device isn't 1G-capable itself. Only look at "Supported link modes" for the card's capabilities.)

It is unfortunately common for Dell Inspiron laptops to only have the 100Mbps variant of the chip, and you will find this mentioned in the spec sheet under "Communications" (direct pdf link).

Spec screenshot

USB 3.x Ethernet adapters (dongles) based on the AX88179 chipset are a reliable alternative.

user1686

Posted 2018-06-30T21:40:48.017

Reputation: 283 655

When running "ethtool" I get this: "Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full". Seems you're right. – B.Cakir – 2018-07-01T09:11:58.650

Asked: 2018-06-30T21:40:48.017

Viewed: 746 times

Active: 2018-07-01T08:46:07.197