Renewal of the DHCP lease causes an interface down/up event

[Christian Zahl]

Based on a DHCPACK the client receives it determines a renewal time, which is 1/2 (+- some randomness) of the lease time provided by the DHCP server. After this time the client sends a new DHCPREQUEST. In my case the same DHCP server responds while providing the same IP address (in my case preconfigured in a customer environment). This one is being reassigned to the interface, resulting in a short link down / link up sequence (see syslog below):

Jan 17 16:52:25 krombacher dhclient[2053]: DHCPREQUEST of 10.225.6.25 on wlan0 to 10.225.6.1 port 67 (xid=0x########)
Jan 17 16:52:25 krombacher dhclient[2053]: DHCPACK of 10.225.6.25 from 10.225.6.1
Jan 17 16:52:25 krombacher NetworkManager[1301]: <info> [1516204345.1307] address 10.225.6.25
Jan 17 16:52:25 krombacher NetworkManager[1301]: <info> [1516204345.1307] plen 24 (255.255.255.0)
Jan 17 16:52:25 krombacher NetworkManager[1301]: <info> [1516204345.1307] gateway 10.225.6.1
Jan 17 16:52:25 krombacher NetworkManager[1301]: <info> [1516204345.1307] server identifier 10.225.6.1
Jan 17 16:52:25 krombacher NetworkManager[1301]: <info> [1516204345.1307] lease time 10800
Jan 17 16:52:25 krombacher vmnet-natd: RTM_NEWADDR: index:3, addr:10.225.6.25
Jan 17 16:52:25 krombacher NetworkManager[1301]: <info> [1516204345.1307] hostname 'krombacher'
Jan 17 16:52:25 krombacher NetworkManager[1301]: <info> [1516204345.1307] nameserver '8.8.8.8'
Jan 17 16:52:25 krombacher NetworkManager[1301]: <info> [1516204345.1307] nameserver '8.8.4.4'
Jan 17 16:52:25 krombacher NetworkManager[1301]: <info> [1516204345.1307] dhcp4 (wlan0): state changed bound -> bound
Jan 17 16:52:25 krombacher dbus[1216]: [system] Activating via systemd: service name='org.freedesktop.nm_dispatcher' unit='dbus-org.freedesktop.nm-dispatcher.service'
Jan 17 16:52:25 krombacher dhclient[2053]: bound to 10.225.6.25 -- renewal in 4326 seconds.
Jan 17 16:52:25 krombacher systemd[1]: Starting Network Manager Script Dispatcher Service...
Jan 17 16:52:25 krombacher dbus[1216]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
Jan 17 16:52:25 krombacher systemd[1]: Started Network Manager Script Dispatcher Service.
Jan 17 16:52:25 krombacher nm-dispatcher: req:1 'dhcp4-change' [wlan0]: new request (1 scripts)
Jan 17 16:52:25 krombacher nm-dispatcher: req:1 'dhcp4-change' [wlan0]: start running ordered scripts...
Jan 17 16:52:25 krombacher kernel: [29622.756223] userif-3: sent link down event.
Jan 17 16:52:25 krombacher kernel: [29622.756227] userif-3: sent link up event.

As a side effect, my running Cisco Connect Anywhere VPN client gets a disconnect event and reconnects again. This will cause a drop of all my open ssh, vnc, Oracle, ... sessions.

Isn't it possible to identify that the IP address is the same as the one currently set and to skip this rebinding procedure?

System details:
lsb_release -rd
Description: Ubuntu 16.04.3 LTS
Release: 16.04

isc-dhcp-client/xenial-updates,now 4.3.3-5ubuntu12.7
isc-dhcp-common/xenial-updates,now 4.3.3-5ubuntu12.7

Thanks,
Christian

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.