Configurando o Squid 2.7 (Proxy Transparente) - Debian Lenny

Abra o arquivo /etc/squid/squid.conf e atualize para: 

# Configuração Geral
#*******************
#
http_port 3128 transparent
cache_mem 32 MB
cache_dir ufs /var/spool/squid 100 16 256
cache_access_log /var/log/squid/access.log
cache_log /var/log/squid/cache.log
cache_store_log /var/log/squid/store.log
pid_filename /var/run/squid.pid
error_directory /usr/share/squid/errors/Portuguese
emulate_httpd_log on
visible_hostname servidor.4pef
cache_mgr taylor@pop.com.br
#
# acl - Recomendadas
#*******************
#
acl all src 0.0.0.0/0.0.0.0
acl manager proto cache_object
acl localhost src 127.0.0.1/255.255.255.255
acl to_localhost dst 127.0.0.0/8
acl SSL_ports port 443 563 # https, snews
acl SSL_ports port 873 # rsync
acl Safe_ports port 80 # http
acl Safe_ports port 21 # ftp
acl Safe_ports port 443 563 # https, snews
acl Safe_ports port 70 # gopher
acl Safe_ports port 210 # wais
acl Safe_ports port 1025-65535 # unregistered ports
acl Safe_ports port 280 # http-mgmt
acl Safe_ports port 488 # gss-http
acl Safe_ports port 591 # filemaker
acl Safe_ports port 777 # multiling http
acl Safe_ports port 631 # cups
acl Safe_ports port 873 # rsync
acl Safe_ports port 901 # SWAT
acl purge method PURGE
acl CONNECT method CONNECT
#
# acl - Personalizadas
#*********************
#
# *** Define portas liberadas
acl Safe_ports port 3050 # Interbase/Firebird
acl Safe_ports port 23000 # Serpro
acl Safe_ports port 13352 # SIRF
acl Safe_ports port 500 # FAP Digital
#
# *** Define a rede interna (Intranet)
acl intranet src 10.0.0.0/255.0.0.0
#
# http_access - Recomendadas
#***************************
#
http_access allow manager localhost
http_access deny manager
http_access allow purge localhost
http_access deny purge
http_access deny !Safe_ports
http_access deny CONNECT !SSL_ports
#
# http_access - Personalizadas
#*****************************
#
# *** Libera dowloads de ate 5 MB
reply_body_max_size 5242880 allow all !admin
#
# Permite acesso da rede interna (Intranet)
http_access allow intranet
#
# *** Nega tudo que não foi liberado ou negado
http_access deny all

Reinicie o squid: 

# squid -k reconfigure
(atualiza sem parar o serviço) 

Ou: 

# /etc/init.d/squid restart