FBSD gateway/firewall with squid <-will it let request in??

[keith at smmc.qld.edu.au]

Hi all,
shooting blind here cause I trouble shoot this (although I am remote from
the systems in question)

            203.111.111.216/29 <-NAT-> 10.0.0.1        10.0.0.2
Internet<------>FBSD (ipfilter/ipnat squid) <------> www/mail server

All "live ips" are alias to external interface of FBSD they NAT to internals.
I have never had squid proxy on a gateway like this. Would squid by
default (I have changed very little in squid.conf) interfere with
externally incoming traffic being Natted to the inside server? Will it
block?
I know this is FBSD not SQUID but maybe it is an ipf hassle otherwise.
Thanks if you can help
Keith