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DHCP gets NAK from a ghost apperently...
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Hexorg
Tux's lil' helper
Tux's lil' helper


Joined: 29 Oct 2009
Posts: 114

PostPosted: Sat Feb 26, 2011 12:51 pm    Post subject: DHCP gets NAK from a ghost apperently... Reply with quote

Hello. I live in the dorms where internet access is delivered through some routers(IP: 10.1.1.1) to the rooms. From there, I used to have my own router,(PI: 192.168.2.1) connecting 4 of my computers. Recently that router stopped working, so I unplugged it, and plugged my gentoo box laptop directly into the wall socket of the dorm's router, however, I can't seem to make dhcpcd use the lease. The offer comes from it, but so does a NAK from 192.168.2.1... but router is unplugged... IT'S HAUNTING ME!!!!

Anyway, I guess it has maybe to do with some dhcpcd caching of some sort? I tried to delete .info and lease files for eth0, but nothing helps. Here's dhcpcd -d eth0:

Code:
/ #dhcpcd -d eth0
dhcpcd[7490]: version 5.2.10 starting
dhcpcd[7490]: eth0: using hwaddr 00:23:8b:fb:1c:96
dhcpcd[7490]: eth0: executing `/lib64/dhcpcd/dhcpcd-run-hooks', reason PREINIT
dhcpcd[7490]: eth0: executing `/lib64/dhcpcd/dhcpcd-run-hooks', reason CARRIER
dhcpcd[7490]: eth0: broadcasting for a lease
dhcpcd[7490]: eth0: sending DISCOVER (xid 0x75614e46), next in 4.85 seconds
dhcpcd[7490]: eth0: offered 10.1.2.195 from 10.1.1.1
dhcpcd[7490]: eth0: sending REQUEST (xid 0x75614e46), next in 3.31 seconds
dhcpcd[7490]: eth0: NAK: from 192.168.2.1
dhcpcd[7490]: eth0: executing `/lib64/dhcpcd/dhcpcd-run-hooks', reason NAK
dhcpcd[7490]: eth0: broadcasting for a lease
dhcpcd[7490]: eth0: sending DISCOVER (xid 0x15dad9b8), next in 4.12 seconds
dhcpcd[7490]: eth0: offered 10.1.2.195 from 10.1.1.1
dhcpcd[7490]: eth0: sending REQUEST (xid 0x15dad9b8), next in 4.82 seconds
dhcpcd[7490]: eth0: NAK: from 192.168.2.1
dhcpcd[7490]: eth0: executing `/lib64/dhcpcd/dhcpcd-run-hooks', reason NAK
^Cdhcpcd[7490]: received SIGINT, stopping
dhcpcd[7490]: eth0: removing interface
dhcpcd[7490]: eth0: executing `/lib64/dhcpcd/dhcpcd-run-hooks', reason STOP


I pressed ctrl+c or it'd keep doing that until timeout
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Hu
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Joined: 06 Mar 2007
Posts: 16043

PostPosted: Sat Feb 26, 2011 5:46 pm    Post subject: Reply with quote

Phantoms cannot generate NAKs. You probably have a rogue DHCP server on your network that is incorrectly canceling addresses. You can confirm this by monitoring the actual network traffic with net-analyzer/tcpdump. The address 192.168.2.1 is not that uncommon among devices used on small LANs, so you are probably getting stepped on by somebody else with the same style router that you disconnected. Some DHCP clients can be configured to ignore select servers, which will work around the rogue server, but only for the machines which are configured to ignore it. To fix the problem, you must find and disconnect/reconfigure the rogue DHCP server. If you can determine its MAC address, your local network administrator may be able to map out its physical location. If other students are also affected, that should provide additional motivation for him or her to help you.
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Hexorg
Tux's lil' helper
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Joined: 29 Oct 2009
Posts: 114

PostPosted: Sat Feb 26, 2011 6:43 pm    Post subject: Reply with quote

I just tried connecting windows machine to the same plug, and it worked, wouldn't that mean that it's some setting error?
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TJNII
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Joined: 09 Nov 2003
Posts: 637
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PostPosted: Sun Feb 27, 2011 3:27 am    Post subject: Reply with quote

Not necessarily. I would sniff the traffic with wireshark under both Linux and Windows to see what you are getting on the wire. Windows may just be ignoring the rogue NAK. I would also compare the MAC address of the 192.168.2.1 on the network with your router.
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