How to log remote WWW server IP address

I want to log the IP address of the WWW server from which the content was
get.

Such as, if user send request "http://www.yahoo.com/" to squid, squid
will get the content from host www.yahoo.com, and will log "www.yahoo.com"
to access_log file. But I want the IP address of www.yahoo.com be logged
in the access_log.

How should I do it?

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73 DE BG6CQ                       URL: http://www.ustc.edu.cn/~james
Zhang Huanjie                  E-mail: james@ustc.edu.cn
Computer Science
University of Science and Technology of China