Comment 4 for bug 1314692

The system making the requests was running Ubuntu 14.04 server. It has four Ethernet ports, which were originally called eth0 to eth3; but after a firmware update, udev decided to rename them to em1 to em4. /var/log/syslog had lots of dhclient activity:

$ grep dhclient /var/log/syslog
Apr 30 07:11:33 decathlete2 dhclient: DHCPREQUEST of 10.20.30.60 on eth3 to 10.20.30.1 port 67 (xid=0x2a1ff0ee)
Apr 30 07:11:33 decathlete2 dhclient: DHCPACK of 10.20.30.60 from 10.20.30.1
Apr 30 07:11:33 decathlete2 dhclient: bound to 10.20.30.60 -- renewal in 19137 seconds.
Apr 30 08:49:02 decathlete2 dhclient: message repeated 1425 times: [ DHCPREQUEST of 10.20.30.58 on eth1 to 10.20.30.1 port 67 (xid=0x424c0758)]
Apr 30 08:49:15 decathlete2 dhclient: DHCPREQUEST of 10.20.30.58 on eth1 to 255.255.255.255 port 67 (xid=0x424c0758)
Apr 30 08:58:01 decathlete2 dhclient: message repeated 1400 times: [ DHCPREQUEST of 10.20.30.59 on eth2 to 10.20.30.1 port 67 (xid=0x7cc18273)]
Apr 30 08:58:18 decathlete2 dhclient: DHCPREQUEST of 10.20.30.59 on eth2 to 255.255.255.255 port 67 (xid=0x7cc18273)
Apr 30 10:19:05 decathlete2 dhclient: message repeated 398 times: [ DHCPREQUEST of 10.20.30.58 on eth1 to 255.255.255.255 port 67 (xid=0x424c0758)]
Apr 30 10:19:10 decathlete2 dhclient: DHCPDISCOVER on eth1 to 255.255.255.255 port 67 interval 3 (xid=0x3bd05ae3)
Apr 30 10:19:10 decathlete2 dhclient: DHCPREQUEST of 10.20.30.58 on eth1 to 255.255.255.255 port 67 (xid=0x3bd05ae3)
Apr 30 10:19:10 decathlete2 dhclient: DHCPOFFER of 10.20.30.58 from 10.20.30.1
Apr 30 10:19:10 decathlete2 dhclient: DHCPACK of 10.20.30.58 from 10.20.30.1
Apr 30 10:19:11 decathlete2 dhclient: bound to 10.20.30.58 -- renewal in 20622 seconds.
Apr 30 10:28:06 decathlete2 dhclient: message repeated 388 times: [ DHCPREQUEST of 10.20.30.59 on eth2 to 255.255.255.255 port 67 (xid=0x7cc18273)]
Apr 30 10:28:09 decathlete2 dhclient: DHCPDISCOVER on eth2 to 255.255.255.255 port 67 interval 3 (xid=0x2d134628)
Apr 30 10:28:09 decathlete2 dhclient: DHCPREQUEST of 10.20.30.59 on eth2 to 255.255.255.255 port 67 (xid=0x2d134628)
Apr 30 10:28:09 decathlete2 dhclient: DHCPOFFER of 10.20.30.59 from 10.20.30.1
Apr 30 10:28:09 decathlete2 dhclient: DHCPACK of 10.20.30.59 from 10.20.30.1
Apr 30 10:28:10 decathlete2 dhclient: bound to 10.20.30.59 -- renewal in 18798 seconds.
Apr 30 10:44:19 decathlete2 dhclient: DHCPREQUEST of 10.20.30.57 on em0 to 10.20.30.1 port 67 (xid=0x6d441934)
Apr 30 12:30:30 decathlete2 dhclient: DHCPREQUEST of 10.20.30.60 on eth3 to 10.20.30.1 port 67 (xid=0x2a1ff0ee)
Apr 30 12:30:30 decathlete2 dhclient: DHCPACK of 10.20.30.60 from 10.20.30.1
Apr 30 12:30:30 decathlete2 dhclient: bound to 10.20.30.60 -- renewal in 19290 seconds.
Apr 30 15:41:28 decathlete2 dhclient: DHCPREQUEST of 10.20.30.59 on eth2 to 10.20.30.1 port 67 (xid=0x2d134628)

I've shut it down for the moment, but will bring it up again soon to experiment, and with any luck find the cause of dhclient going berserk.