How to keep only IP of client into log?

["chowalit.lab Chowalit Lab Linux" <chowalit.lab@xxxxxxxxx>]

Hi all,
      On my system that is squid 2.6 on centos 5 with default
logformat configuration. In access.log, it keep hostname of client
instead of IP of client. I don't like this format because I have log
analyzer that read only IP format.  Which option use to change format
of logfile that keep only IP of client.

Thanks
Chong