View Full Version : IP Configuration in use by...

Jun 12, 2010, 07:53 PM
Our network has been working fine up until now. We have an xserve, a switch off of an xserve that shoots out the internet to all of our ethernet ports in the school. After a couple weeks (school got out and went on vaca) I came back and logged on to a couple of the computers in the computer lab and got this message on each computer. IP Configuration: XXX.XXX.X.XX in use by XX:XX:XX:XX:XX:XX, DHCP Server XXX.XXX.X.X. Of course the IP's were different on each computer I tried. THis message has never popped up before. Our printers are also being very strange, and I am guessing it has to do with this same thing, since our printers are wired via ethernet also.

Can anyone give me some ideas on this? Thanks so much. I greatly need the help and very much appreciate anything.

Jun 13, 2010, 09:22 AM
I'd be interested to hear any ideas on this as well. Our Xserve does similar.

Jun 13, 2010, 09:59 AM
The first thing to do is see what your system thinks is out there. This is done with the arp command (ip and MAC addressess are fudged):

# arp -a
gateway.xxxx.com ( at 0:90:1a:a1:5b:93 on en0 ifscope [ethernet]
? (( at ff:ff:ff:ff:ff:ff on en0 ifscope [ethernet]
? ( at 90:84:d:d3:e2:cf on en1 ifscope [ethernet]
nekokun.internalnetwork.com ( at 0:1f:f3:d4:ac:43 on en1 ifscope [ethernet]
? ( at ff:ff:ff:ff:ff:ff on en1 ifscope [ethernet]

Then check this list for a duplicate of your host (I don't have one but you do. To find out what the addresses your host uses, use the ifconfig command:

# ifconfig -a
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
inet6 ::1 prefixlen 128
inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1
inet netmask 0xff000000
gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280
stf0: flags=0<> mtu 1280
ether 00:19:e3:f9:34:c9
inet netmask 0xffffff00 broadcast
inet netmask 0xffffff00 broadcast
inet netmask 0xffffff00 broadcast
inet netmask 0xffffff00 broadcast
inet netmask 0xffffff00 broadcast
inet netmask 0xffffff00 broadcast
media: autoselect (1000baseT <full-duplex,flow-control>)
status: active
ether 00:19:e3:ba:ab:bc
inet6 fe80::219:feef:abc1:5ba3%en1 prefixlen 64 scopeid 0x5
inet netmask 0xffffff00 broadcast
media: autoselect (1000baseT <full-duplex,flow-control>)
status: active
ether 00:19:e3:ab:cd:ef
media: <unknown subtype> (<unknown type>)
status: inactive
lladdr 00:1b:63:ff:cd:dc:ab:12
media: autoselect <full-duplex>
status: inactive

If it's just a bad arp table, you can delete the entry with arp -d. (see the man page for arp for more details).

Jun 13, 2010, 02:28 PM
are these commands I run in terminal on the server? I majored in IT but this sounds slightly foreign to me.

Jun 13, 2010, 03:40 PM
Yes, you run them from the terminal. They are standard Unix commands. I don't know of any flavour of Unix that doesn't have them (though the arguments may be different so you have to check the man page if you are on a Unix system you're not familiar with). The arp command needs to be run as root.