> Can u post dhclient.conf to see wich parameters your machine 
> asking from
> ISP? ( like send-host-name?)
> 

Thanks for responding.  I discovered that I had no 
dhclient.conf.  Evidently all of the defaults used to 
work because the ISP wasn't sending the host-name (based
on the contents of old copies of /var/db/dhclient.leases).  

I provided a dhclient.conf, making sure not to include
host-name and domain-name in the request list and now
everything seems to be normal again.