ssh without reverse DNS lookup

[Pedro Zorzenon Neto <pzn@terra.com.br>]

Hi,

   ssh in potato is set to always try to use reverse DNS lookup. If the
client is not registered in the DNS server, then it gets an answer:
"ssh_exchange_identification: Connection closed by remote host"

   I've looked in "man sshd" and "man ssh" and I didn't see any
configuration option which bypass the reverse lookup, enabling
connections from machines without reverse DNS lookup. How can I do
this? (I don't want to add each machine to /etc/hosts)

   Which are the security problems when I bypassing this lookup?

   Thanks in advance,
    Pedro