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Old 12-24-2012, 12:08 AM   #1
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Question linux box ethernet not detecting connection to router


I've got really strange issue with eth.

I had router Linksys* E3000*connected to modem. On that router I had linux box connected and many other clients also. Things worked.

Now I replaced Linksys with new router (Asus RT-n66u), connected all things same as before. Everything works (all clients connected) but only this linux box doesn't obtain ip from router. The led on the router doesn't* turn on at all when cable plugged in. The led will turn on when box is restarted but will turn off when booting passes GRUB or so. If I* pause booting at GRUB led will stay on and will turn off when it continues booting.

I checked cable, I tryed all ports on Asus router, I connected the linux box to two other routers - it works fine there and it obtains ip (both routers have different ips).

Network card on the linux box is jmicron jmx251 1gigabit.

Thank you for any help.

Last edited by agatone; 12-24-2012 at 12:09 AM.
Old 12-24-2012, 11:13 AM   #2
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ethtool eth0

command showing link connected : yes

Old 12-24-2012, 12:33 PM   #3
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No, it says:
Link detected: no
Old 12-24-2012, 01:00 PM   #4
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dhclient eth0
Old 12-24-2012, 10:47 PM   #5
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Link detected no claiming that cable is not connected . If you sure that cable is properly connected then I suspect , there could be speed mismatch b/w switch port and ethernet card . Try to set speed using ethtool -s command
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Old 12-25-2012, 12:31 PM   #6
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As I set speed to 100mbit FD it started working. The odd thing is that router is gigabit and so is card, but I can see that router is advertising 100mbit FD max to the linux box.

Gigabit works for sure on both sides (router and linux box) because I successfully connected windows clients at gigabit speed to the router and llinux box can connect to other routers at gigabit too.

Any ideas why would router advertise only 100mbit to the linux box?

Last edited by agatone; 12-25-2012 at 12:55 PM. Reason: better explanation


eth, ethernet, nic, router

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