Topic: How to tell what speed an interface is running?

[Terry]

As the topic says, how can I determine whether an interface is running 10 or 100 Mbps, and is it running full or half duplex.  I just installed a new switch and am wondering if I'm getting everything I can out of it.  And no, the switch doesn't have any management features, so I can't check on that side of things.

[DREi]

Your switch may be unmanaged but the lights on the front indicate 10/100 and Half/Full duplex modes.Terry wrote:
>
> As the topic says, how can I determine whether an interface
> is running 10 or 100 Mbps, and is it running full or half
> duplex.  I just installed a new switch and am wondering if
> I'm getting everything I can out of it.  And no, the switch
> doesn't have any management features, so I can't check on
> that side of things.

[Terry]

DREi wrote:
>
> Your switch may be unmanaged but the lights on the front
> indicate 10/100 and Half/Full duplex modes.Terry wrote:
> >

Nope, just connection and traffic.

[Andy MacDonald]

Have you tried "ifconfig -a" at the command line?

[Terry]

Should I be looking for something specific on the interface?  Doesn't look like it shows much more then what ifconfig does, unless this line means something...
EtherTalk Phase 2 addr:65280/28
Other then that I don't see anything that may confirm the interface is running 10 or 100 Megs.

[Scott Smith]

mii-tool

--or--

mii-tool  -v

[Terry]

Thanks Scott, I think we're almost there.  That command confirms that the card will do 100Meg (which I was only 95% sure it would), but is there anything here that confirms it IS running 100?

[root@pdc root]# mii-tool  -v
eth0: negotiated 100baseTx-FD flow-control, link ok
  product info: vendor 00:10:18, model 23 rev 6
  basic mode:   autonegotiation enabled
  basic status: autonegotiation complete, link ok
  capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  advertising:  100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control
  link partner: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control

[Michiel]

>   link partner: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control

The 'link partner' line lists all the confirmed speeds to the next hop. Hence you have a 100 FD link to your switch. Congratulations

[Byte]

Also....

dmesg |grep eth0

Will give this result

[root@dev root]# dmesg | grep eth0
e100: eth0 NIC Link is Up 100 Mbps Full duplex

HTH Byte

[Scott Smith]

Or...

man mii-tool

[Terry]

Thanks Michiel, Byte, that command doesn't give me any output when I use it.

[Scott Smith]

mii-tool tells you at what speed the interface is running. That's the first line of output -- eth0: negotiated 100baseTx-FD flow-control, link ok.

If you don't trust the output of mii-tool, then you need to trust your link lights, or if you don't have any link lights, then you'll need to attach a sniffer than can tell you the speed, or if you don't have a sniffer, then you can perform a few file transfers and compute the speed.

[Terry]

I do trust it, hence the thanks to Michael, which I now see should have been to both of you.  Thanks Scott.  And I totally missed the "negotiated" line the 1st time.  Thanks again.