SQUID is a high‐performance proxy caching server for web clients, supporting FTP, gopher, and HTTP data objects etc. By default it listen on TCP 3128 port. Following iptables rules allows SQUID incoming client request (open TCP port 3128) for server IP address 202.54.1.20:
iptables -A INPUT -p tcp -s 0/0 --sport 1024:65535 -d 202.54.1.20 --dport 3128 -m state --state NEW,ESTABLISHED -j ACCEPT

iptables -A OUTPUT -p tcp -s 202.54.1.20 --sport 3128 -d 0/0 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT