We have nearly 50 systems with windows XP and have Linux (RHEL6) for server.Also have squid 3.1 , Samba and Apache for local use.Under proxy, VPN and outlook express does not connected. I heard that transparent proxy will fix this problem. I have tried steps from internet and stack-exchange. But i can't fix this issue fully. Please give clear configuration file and configuration for IpTables.Here my squid conf file.## Recommended minimum configuration:#acl manager proto cache_objectacl localhost src 127.0.0.1/32 ::1acl to_localhost dst 127.0.0.0/8 0.0.0.0/32 ::1## Example rule allowing access from your local networks.# Adapt to list your (internal) IP networks from where browsing# should be allowedacl localinternet src 10.1.1.0/24##acl localnet src 10.0.0.0/8        # RFC1918 possible internal network##acl localnet src 172.16.0.0/12    # RFC1918 possible internal network##acl localnet src 192.168.0.0/16    # RFC1918 possible internal network##acl localnet src fc00::/7           # RFC 4193 local private network range##acl localnet src fe80::/10          # RFC 4291 link-local (directly plugged) machines## Special IP Listacl special src /etc/squid/special.txt                # All Access IPs# Allowed IP Listacl d_unlimited src /etc/squid/d_unlimited.txt        # Full Download accessacl u_unlimited src /etc/squid/u_unlimited.txt        # Full Upload accessacl allow_proxy src /etc/squid/allow_proxy.txt        # Allow Proxyacl allow_social src /etc/squid/allow_social.txt      # Allow Social networkingacl allow_tutorial src /etc/squid/allow_tutorial.txt  # Allow Tutorialacl allow_movie src /etc/squid/allow_movie.txt        # Allow Jobsacl allow_jobs src /etc/squid/allow_jobs.txt          # Allow Movieacl allow_sex src /etc/squid/allow_sex.txt            # Allow Sex## Blocked Keys#acl goodkey url_regex /etc/squid/goodkey.txtacl proxy url_regex /etc/squid/proxy.txtacl social url_regex /etc/squid/social.txtacl tutorial url_regex /etc/squid/tutorial.txtacl movie url_regex /etc/squid/movie.txtacl jobs url_regex /etc/squid/jobs.txtacl sex url_regex /etc/squid/sex.txt## Upload/Download Limit#request_body_max_size 2000 KB localinternet !u_unlimitedreply_body_max_size 6000 KB localinternet !d_unlimited##acl SSL_ports port 443acl Safe_ports port 80        # httpacl Safe_ports port 21        # ftpacl Safe_ports port 443        # httpsacl Safe_ports port 70        # gopheracl Safe_ports port 210        # waisacl Safe_ports port 1025-65535    # unregistered portsacl Safe_ports port 280        # http-mgmtacl Safe_ports port 488        # gss-httpacl Safe_ports port 591        # filemakeracl Safe_ports port 777        # multiling httpacl CONNECT method CONNECT## Recommended minimum Access Permission configuration:## Only allow cachemgr access from localhosthttp_access allow manager localhosthttp_access deny manager# Deny requests to certain unsafe portshttp_access deny !Safe_ports# Deny CONNECT to other than secure SSL portshttp_access deny CONNECT !SSL_ports# We strongly recommend the following be uncommented to protect innocent# web applications running on the proxy server who think the only# one who can access services on localhost is a local user#http_access deny to_localhost## INSERT YOUR OWN RULE(S) HERE TO ALLOW ACCESS FROM YOUR CLIENTS## Example rule allowing access from your local networks.# Adapt localnet in the ACL section to list your (internal) IP networks# from where browsing should be allowed#http_access allow localnet## Allow all / Allow Good keyshttp_access allow specialhttp_access allow goodkey## Allow  Proxy Sites#http_access allow allow_proxy proxy## Allow Social Networking#http_access allow allow_social social## Allow Tutorialshttp_access allow allow_tutorial tutorial## Allow Moviehttp_access allow allow_movie movie## Allow Jobshttp_access allow allow_jobs jobs## Allow Sexhttp_access allow allow_sex sex## Allow Listhttp_access allow localinternet !proxy !social !tutorial !movie !jobs !sex## Local Hosthttp_access allow localhost# And finally deny all other access to this proxyhttp_access deny all# Squid normally listens to port 3128http_port 3128# We recommend you to use at least the following line.hierarchy_stoplist cgi-bin ?# Uncomment and adjust the following to add a disk cache directory.#cache_dir ufs /var/spool/squid 100 16 256# Leave coredumps in the first cache dircoredump_dir /var/spool/squid# Add any of your own refresh_pattern entries above these.refresh_pattern ^ftp:        1440    20%    10080refresh_pattern ^gopher:    1440    0%    1440refresh_pattern -i (/cgi-bin/|\?) 0    0%    0refresh_pattern .        0    20%    4320
Transparent proxy with squid 3.1 on RHEL 6
linux;rhel;proxy;squid