Pb pour faire marcher mon squid transparent

Bonjour,

voici mon squid.conf

/etc/squid3/squid.conf:acl manager proto cache_object
/etc/squid3/squid.conf:acl localhost src 127.0.0.1/32 ::1
/etc/squid3/squid.conf:acl allowedips src 192.168.21.0/255.255.255.0
/etc/squid3/squid.conf:acl to_localhost dst 127.0.0.0/8 0.0.0.0/32 ::1

/etc/squid3/squid.conf:acl localnet src 192.168.21.0/24

/etc/squid3/squid.conf:acl SSL_ports port 443
/etc/squid3/squid.conf:acl Safe_ports port 80 # http
/etc/squid3/squid.conf:acl Safe_ports port 21 # ftp
/etc/squid3/squid.conf:acl Safe_ports port 443 # https
/etc/squid3/squid.conf:acl Safe_ports port 70 # gopher
/etc/squid3/squid.conf:acl Safe_ports port 210 # wais
/etc/squid3/squid.conf:acl Safe_ports port 1025-65535 # unregistered ports
/etc/squid3/squid.conf:acl Safe_ports port 280 # http-mgmt
/etc/squid3/squid.conf:acl Safe_ports port 488 # gss-http
/etc/squid3/squid.conf:acl Safe_ports port 591 # filemaker
/etc/squid3/squid.conf:acl Safe_ports port 777 # multiling http
/etc/squid3/squid.conf:acl CONNECT method CONNECT

/etc/squid3/squid.conf:http_access allow manager localhost
/etc/squid3/squid.conf:http_access deny manager

/etc/squid3/squid.conf:http_access deny !Safe_ports

/etc/squid3/squid.conf:http_access deny CONNECT !SSL_ports

/etc/squid3/squid.conf:http_access allow localnet
/etc/squid3/squid.conf:http_access allow localhost
/etc/squid3/squid.conf:http_access allow allowedips

/etc/squid3/squid.conf:http_port 3128 transparent

/etc/squid3/squid.conf:hierarchy_stoplist cgi-bin ?

/etc/squid3/squid.conf:cache_mem 16 MB

/etc/squid3/squid.conf:maximum_object_size_in_memory 15 KB

/etc/squid3/squid.conf:cache_dir ufs /var/spool/squid3 100 16 256

/etc/squid3/squid.conf:cache_swap_low 90
/etc/squid3/squid.conf:cache_swap_high 95

/etc/squid3/squid.conf:coredump_dir /var/spool/squid3

/etc/squid3/squid.conf:refresh_pattern ^ftp: 1440 20% 10080
/etc/squid3/squid.conf:refresh_pattern ^gopher: 1440 0% 1440
/etc/squid3/squid.conf:refresh_pattern -i (/cgi-bin/|\?) 0 0% 0
/etc/squid3/squid.conf:refresh_pattern . 0 20% 4320

/etc/squid3/squid.conf:positive_dns_ttl 8 hours

/etc/squid3/squid.conf:negative_dns_ttl 1 minutes

/etc/squid3/squid.conf:cache_effective_user proxy

/etc/squid3/squid.conf:cache_effective_group root

/etc/squid3/squid.conf:visible_hostname fred-ubuntu

/etc/squid3/squid.conf:error_directory /usr/share/squid3/errors/French

/etc/squid3/squid.conf:forwarded_for off

/etc/squid3/squid.conf:cache_effective_group root

ET AUSI MON IPTABLE

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -j REDIRECT --to-port 3128

pourriez vous me dire pour quoi il fonctionne pas ?
merci