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Old 07-02-2004, 07:37 AM   #1
Registered: Nov 2003
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How can i see if an ethernet interface is physically up/down ?

I am using LINUX with a 4 port ethernet interface.

I login via telnet via one of the 4 ports.

Is there a command that tells me whether or not the physical link on interfaces is up / down ?

I tried ifconfig -a, but I do not see any difference between a port where the physical link is up and a port where the physical link is down.
Old 07-02-2004, 07:49 AM   #2
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if all your int's are on the same subnet (unless there is routing) you can ping 'em...
if ping is successful int is UP.

if you don't know if int is physically UP but has no IP assigned (so you can't ping it) check your RX/TX output
in 'ifconfig'.
[#| ifconfig -a eth2 (so you only get info for the specs. on eth2...)]
EDIT: maybe the -a param. is ambiguous... cause this means: show ALL interfaces no matter if UP/DOWN...

every int sends/recieves bcast packets every once in a while, no matter if an IP has been assigned or not.

so if the count on bcast packets increases you know the int is physically UP...

this of course does not matter if there is no media attached to the int, so this hint is not multi-purpose... ;-)

also i came up with the idea of 'ethtool'. this shows an output that marks the state of an int.

hope it helps...


please sign here!

Last edited by tom_on_linux; 07-02-2004 at 08:33 AM.
Old 07-02-2004, 09:50 AM   #3
Registered: Nov 2003
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I tried ethtool but unfortunately my card is not supported (no data available).

However, I tried it on another machine (wiht other NIC offcourse) and I must say that ethtool is very usable when your NIC is supported.

Are there any other commands possible, except the packet counters from ifconfig -a ?
Old 07-02-2004, 12:39 PM   #4
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mii-tool ?
Old 07-02-2004, 03:06 PM   #5
Registered: Nov 2003
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mii-tool is perfect and works on the NIC where ethtool didn't.

Thanks !


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