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I told datacenter too connect two of my servers with a crossover cable to each other. But when I try this command
ethtool eth0

Settings for eth0:
        Supported ports: [ TP ]
        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: Unknown!
        Duplex: Unknown! (255)
        Port: Twisted Pair
        PHYAD: 2
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: pumbg
        Wake-on: g
        Current message level: 0x00000001 (1)
        Link detected: no

"Link detected: no" shows that network is unplugged. is there something wrong with my network adaptor? or is there other possiblities like driver problem and etc?
I am posting eth1 information too maybe it will be usefull.(conflict with eth0 maybe)

ethtool eth1
Settings for eth1:
        Supported ports: [ TP ]
        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
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: pumbg
        Wake-on: g
        Current message level: 0x00000001 (1)
        Link detected: yes

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closed as not constructive by Sirex, mdpc, Ward, Dave M, TheCleaner Feb 8 '13 at 15:05

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2 Answers 2

up vote 5 down vote accepted

I told datacenter too connect two of my servers with a crossover cable to each other.

1998 called. They want their cable back.

These are Gigabit ports. Gigabit ports don't have send and receive lines and a crossover cable should never be used on one (unless you know exactly what you're doing). A regular category 5e or category 6 straight through cable with legal GE pin-to-pair assignments must be used. Use the same cable you'd use to connect a Gigabit Ethernet station to a Gigabit switch port.

(There is actually a specification for a Gigabit crossover cable, but odds are that wasn't what was used and there's no need since you can't find a Gigabit port without auto-MDI/MDI-X.)

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Gigabit ports will fall back to 100M if and when required and will work with crossover cables. –  John Gardeniers Feb 8 '13 at 8:04
    
True, but it's still a really dumb thing to do. –  David Schwartz Feb 8 '13 at 8:09
2  
I'm not questioning the dumbness, merely the technical accuracy. ;) –  John Gardeniers Feb 8 '13 at 8:13

The network adapter is reporting no link to the OS, and the link light on the NIC is probably off too.

Bad NICs, bad cables, cables that aren't plugged in all the way.. maybe the cables got plugged into the wrong spot.. all of these things are possibilities.

You'll need to do troubleshooting to eliminate possibilities - I'd start with getting verification that the cable was plugged in to the right place and whether the staff on site are seeing link lights on both ends.

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3  
As soon as I read I told datacenter too connect two of my servers with a crossover cable my first thought was "They screwed it up". It wouldn't be the first time a monkey didn't do quite the right thing... –  Mark Henderson Feb 8 '13 at 1:04

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