All of a sudden the network at my University has frozen and we managed to isolate the problem to massive amounts of UDP packets sent on the DHCP ports. On closer inspection, we found that some of the clients keep spamming the server with DHCP requests although the server seem to respond. I'm pasting a sample of the syslog file on the server ([[client IP]] is the same in all entries, the server and client IP are in the same subnet). The very odd thing is that it's not only one client that does this, there is even a wireless router and it just started happening today. isc-dhcp-server doesn't seen to have been updated. Any assistance would be greatly appreciated.
Feb 25 17:57:46 zeus dhcpd: DHCPRELEASE of [[client IP]] from 00:22:75:ea:e5:dc via eth1 (found)
Feb 25 17:57:48 zeus dhcpd: message repeated 3 times: [ DHCPRELEASE of [[client IP]] from 00:22:75:ea:e5:dc via eth1 (found)]
Feb 25 17:57:48 zeus dhcpd: DHCPDISCOVER from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:49 zeus dhcpd: DHCPOFFER on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:50 zeus dhcpd: DHCPDISCOVER from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:50 zeus dhcpd: DHCPOFFER on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:50 zeus dhcpd: DHCPREQUEST for [[client IP]] ([[server IP]]) from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:50 zeus dhcpd: DHCPACK on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPDISCOVER from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPOFFER on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPREQUEST for [[client IP]] ([[server IP]]) from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPACK on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPDISCOVER from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPOFFER on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPREQUEST for [[client IP]] ([[server IP]]) from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPACK on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPDISCOVER from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPOFFER on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPREQUEST for [[client IP]] ([[server IP]]) from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPACK on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPDISCOVER from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPOFFER on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPREQUEST for [[client IP]] ([[server IP]]) from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:51 zeus dhcpd: DHCPACK on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:52 zeus dhcpd: DHCPDISCOVER from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:52 zeus dhcpd: DHCPOFFER on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:52 zeus dhcpd: DHCPREQUEST for [[client IP]] ([[server IP]]) from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:52 zeus dhcpd: DHCPACK on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:52 zeus dhcpd: DHCPDISCOVER from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:52 zeus dhcpd: DHCPOFFER on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:52 zeus dhcpd: DHCPREQUEST for [[client IP]] ([[server IP]]) from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:52 zeus dhcpd: DHCPACK on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:53 zeus dhcpd: DHCPDISCOVER from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:53 zeus dhcpd: DHCPOFFER on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:53 zeus dhcpd: DHCPREQUEST for [[client IP]] ([[server IP]]) from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:53 zeus dhcpd: DHCPACK on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:53 zeus dhcpd: DHCPDISCOVER from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:53 zeus dhcpd: DHCPOFFER on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:53 zeus dhcpd: DHCPREQUEST for [[client IP]] ([[server IP]]) from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:53 zeus dhcpd: DHCPACK on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:53 zeus dhcpd: DHCPDISCOVER from 00:22:75:ea:e5:dc via eth1
Feb 25 17:57:53 zeus dhcpd: DHCPOFFER on [[client IP]] to 00:22:75:ea:e5:dc via eth1
Contents of /var/lib/dhcp/dhcpd.leases:
lease [[client IP]] {
starts 4 2016/02/25 16:06:25;
ends 5 2016/02/26 16:06:25;
cltt 4 2016/02/25 16:06:25;
binding state active;
next binding state free;
rewind binding state free;
hardware ethernet 00:22:75:ea:e5:dc;
uid "\001\000\"u\352\345\334";
}
lease [[client IP]] {
starts 4 2016/02/25 16:06:25;
ends 5 2016/02/26 16:06:25;
cltt 4 2016/02/25 16:06:25;
binding state active;
next binding state free;
rewind binding state free;
hardware ethernet 00:22:75:ea:e5:dc;
uid "\001\000\"u\352\345\334";
}
lease [[client IP]] {
starts 4 2016/02/25 16:06:26;
ends 5 2016/02/26 16:06:26;
cltt 4 2016/02/25 16:06:26;
binding state active;
next binding state free;
rewind binding state free;
hardware ethernet 00:22:75:ea:e5:dc;
uid "\001\000\"u\352\345\334";
}
lease [[client IP]] {
starts 4 2016/02/25 16:06:27;
ends 4 2016/02/25 16:08:53;
tstp 4 2016/02/25 16:08:53;
cltt 4 2016/02/25 16:06:27;
binding state free;
hardware ethernet 00:22:75:ea:e5:dc;
uid "\001\000\"u\352\345\334";
}
lease [[client IP]] {
starts 4 2016/02/25 16:08:57;
ends 5 2016/02/26 16:08:57;
cltt 4 2016/02/25 16:08:57;
binding state active;
next binding state free;
rewind binding state free;
hardware ethernet 00:22:75:ea:e5:dc;
uid "\001\000\"u\352\345\334";
}
lease [[client IP]] {
starts 4 2016/02/25 16:08:57;
ends 4 2016/02/25 16:08:57;
tstp 4 2016/02/25 16:08:57;
cltt 4 2016/02/25 16:08:57;
binding state free;
hardware ethernet 00:22:75:ea:e5:dc;
uid "\001\000\"u\352\345\334";
}
lease [[client IP]] {
starts 4 2016/02/25 16:08:57;
ends 5 2016/02/26 16:08:57;
cltt 4 2016/02/25 16:08:57;
binding state active;
next binding state free;
rewind binding state free;
hardware ethernet 00:22:75:ea:e5:dc;
uid "\001\000\"u\352\345\334";
}
lease [[client IP]] {
starts 4 2016/02/25 16:08:57;
ends 4 2016/02/25 16:08:57;
tstp 4 2016/02/25 16:08:57;
cltt 4 2016/02/25 16:08:57;
binding state free;
hardware ethernet 00:22:75:ea:e5:dc;
uid "\001\000\"u\352\345\334";
}
Best Answer
You might see this behavior if communication is only going one way between these clients and the DHCP server.
The requests make it through to the server, the server responds but the client never gets the response. So it keeps asking.
I have seen this happen due to damaged cabling. So the first thing I would try is giving one of the clients an appropriate static IP address and seeing if it can actually ping the DHCP server and get a response.