I use dhcp in /etc/network/interfaces:

auto eth0
iface eth0 inet dhcp
No network-manager installed.

This makes the dhclient run with option "-1":
dhclient3 -e IF_METRIC=100 -pf /var/run/dhclient.eth0.pid -lf /var/lib/dhcp/dhclient.eth0.leases -1 eth0
dhclient manpage:
The -1 flag will cause dhclient to try once to get a lease. If it fails, dhclient exits with exit code two.When the dhcpd server is not reachable, the client exits after "No DHCPOFFERS received".

I want the dhclient keep running to get a new ip address when the dhcpd server is reachable again.

How can I configure this?