Re: Ethernet Port Speed

[Guy Harris <guy () alum mit edu>]

On Sep 8, 2012, at 10:53 AM, Ed Stuart <fcache () gmail com> wrote:

> I'm a newbie and I need to know if I can determine port speed settings of an ethernet port.

If you're logged into the machine with the Ethernet port, then there's probably a command and/or GUI tool to do so; 
what tool it is depends on the operating system.

In at least some versions of some BSD-flavored OSes, including recent versions of OS X, the ifconfig command will 
report that:

        $ ifconfig en0
        en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
                options=b<RXCSUM,TXCSUM,VLAN_HWTAGGING>

                        ...

                media: autoselect (1000baseT <full-duplex>)
                status: active

(OS X Lion - on a virtual machine, so it's not "really" gigabit, but the same thing happens on real interfaces; the 
host machine doesn't have an Ethernet interface so I can't try it)

        $ ifconfig em0
        em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
                options=9b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM>

                        ...

                media: Ethernet autoselect (1000baseTX <full-duplex>)
                status: active

(FreeBSD 7.3, again on a virtual machine), but some versions of some OSes might not support it (NetBSD 5.1 didn't show 
the speed, for example).

In Windows XP, the Network Connections item in the Control Panel lets you see the properties of a "network connection"; 
these include the speed of the Ethernet port (at least on my virtual machine).  The ipconfig command, at least when run 
with /all, didn't report anything, but I guess that's not part of the IP configuration; I don't know if there's a 
command that will report it.  Windows 7 is similar, except that it's "Network and Sharing Center" rather than "Network 
Connections" in Control Panel.

As Ilias el Matani noted in his reply, in Linux you can use the ethtool command (which, at least on my Ubuntu 7.10 
machine, had to be run as root - unlike ifconfig on *BSD/OS X):

        $ sudo ethtool eth2
        Settings for eth2:

                        ...

                Supported link modes:   10baseT/Half 10baseT/Full 
                                        100baseT/Half 100baseT/Full 
                                        1000baseT/Full 
                Supports auto-negotiation: Yes
                Advertised link modes:  10baseT/Half 10baseT/Full 
                                        100baseT/Half 100baseT/Full 
                                        1000baseT/Full 
                Advertised auto-negotiation: Yes
                Speed: 1000Mb/s

                        ...

ifconfig doesn't report the speed on my Solaris 10 virtual machine; neither AIX nor HP-UX run on PCs, so I have no 
virtual machines for them on which to try this.
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