configure PG clients for DNS

Hello Pg Gurus,
I would like to know how can I  configure  PG clients in pg_hba.conf to
use DNS entries ( aka domain/host names) insted of  ip's/CIDR-ADDRESS .
my env: PG version 8.3.6 on RHES 5.1
Thank you
Isabella

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Isabella A. Ghiurea

Isabella.Ghiurea@nrc-cnrc.gc.ca
Canadian Astronomy Data Centre | http://www1.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/
National Research Council of Canada, Herzberg Institute of Astrophysics
5071 West Saanich Road, Victoria BC V9E 2E7, Canada
Phone: 250 363-3446 fax: 250 363-0045