wifi, dhclient and pdnsd, after connection reestablished dns server refuses

Hello,
I run a laptop with wifi, dhclient and pdnsd. I have a poor signal,
and the wifi sometimes
looses connection and regains it. The eventlog looks like this:

Jul 12 17:35:43 lh ifplugd(ath0)[5650]: Link beat detected.
Jul 12 17:35:44 lh ifplugd(ath0)[5650]: Link beat lost.
Jul 12 17:35:46 lh kernel: ADDRCONF(NETDEV_CHANGE): ath0: link becomes
ready
Jul 12 17:35:46 lh kernel: ADDRCONF(NETDEV_CHANGE): ath0: link becomes
ready
Jul 12 17:35:47 lh dhclient: DHCPDISCOVER on ath0 to 255.255.255.255
port 67 interval 3
Jul 12 17:35:48 lh kernel: ADDRCONF(NETDEV_CHANGE): ath0: link becomes
ready
Jul 12 17:35:48 lh kernel: ADDRCONF(NETDEV_CHANGE): ath0: link becomes
ready
Jul 12 17:35:51 lh dhclient: DHCPDISCOVER on ath0 to 255.255.255.255
port 67 interval 5
Jul 12 17:35:51 lh kernel: ADDRCONF(NETDEV_CHANGE): ath0: link becomes
ready
Jul 12 17:35:51 lh kernel: ADDRCONF(NETDEV_CHANGE): ath0: link becomes
ready
Jul 12 17:35:54 lh kernel: ADDRCONF(NETDEV_CHANGE): ath0: link becomes
ready
Jul 12 17:35:54 lh kernel: ADDRCONF(NETDEV_CHANGE): ath0: link becomes
ready
Jul 12 17:35:54 lh ifplugd(ath0)[5650]: Link beat detected.
Jul 12 17:35:55 lh ifplugd(ath0)[5650]: Link beat lost.
Jul 12 17:35:55 lh dhclient: DHCPDISCOVER on ath0 to 255.255.255.255
port 67 interval 5
Jul 12 17:35:57 lh kernel: ADDRCONF(NETDEV_CHANGE): ath0: link becomes
ready
Jul 12 17:35:57 lh kernel: ADDRCONF(NETDEV_CHANGE): ath0: link becomes
ready

In most cases I have to reboot to regain connectivity. Sigh.

Sometimes I get back the connectivity, except that the dns servers
refuse every query.
The servers are some unknown IP addresses; the network belongs to an
institution
and I do not have ready access to the sysadms.

I fix it manually by doing
# pdnsd-ctl server resolvconf down
# pdnsd-ctl server resolvconf up 192.168.1.1

where the specified IP address is the default gateway.

Is there a way to make dhclient to renew the lease and renegotiate the
dns servers?
Is there a way to make pdnsd trigger such renewal when all servers
refuse?

Regards