一、背景：
一台双网卡服务器，安装Ubuntu Server 12.04，网卡 eth0 空置，eth1连接局域网，IP 192.168.1.1/24，先连接了宽带路由器。
二、Squid3
尝试源码安装当前最新的Squid3.3，遇到很多问题，懒得弄了，用Ubuntu源里的3.1.19吧。
$sudo apt-get install squid3
配置文件在 /etc/squid3/squid.conf，这个配置文件包含详细的说明，总共5700多行，备份一份出来仔细研究吧，再从百度、Bing、谷歌里搜一搜，最后出来这么个配置文件：
acl alldst dst all
acl manager proto cache_object
acl localhost src 127.0.0.1/32 ::1
acl to_localhost dst 127.0.0.0/8 0.0.0.0/32 ::1
acl localnet src 192.168.1.0/16 # 修改后的
acl SSL_ports port 443
acl Safe_ports port 80 # http
acl Safe_ports port 21 # ftp
acl Safe_ports port 443 # https
acl Safe_ports port 70 # gopher
acl Safe_ports port 210 # wais
acl Safe_ports port 1025-65535 # unregistered ports
acl Safe_ports port 280 # http-mgmt
acl Safe_ports port 488 # gss-http
acl Safe_ports port 591 # filemaker
acl Safe_ports port 777 # multiling http
acl CONNECT method CONNECT
forwarded_for delete # 修改后的，否则在远程服务器上会收到包含内网IP的 HTTP头数据（X_Forwarded_for）
acl_uses_indirect_client on
delay_pool_uses_indirect_client on
http_access allow manager localhost
http_access deny manager
http_access deny !Safe_ports
http_access deny CONNECT !SSL_ports
http_access allow localnet # 修改后的
http_port 192.168.1.1:3128 # 修改后的
cache_mem 1024 MB #自己看情况设定。
maximum_object_size_in_memory 2048 KB #内存缓存的最大对象。
cache_dir ufs /opt/cache 200000 16 256 #/opt 是个独立分区 240G，分配约200G做cache。
coredump_dir /var/spool/squid3
logformat custcommon %>a [%tl] %3>Hs %8<st %Ss:%Sh %rm "%ru" %mt
access_log /var/log/squid3/access.log custcommon
# logformat logformat squid %ts.%03tu %6tr %>a %Ss/%03>Hs %<st %rm %ru %un %Sh/%<A %mt
# access_log /var/log/squid3/access.log squid
# 这里修改了一下默认的日志格式，更方便阅读。
# 原格式 1361289819.737 21 192.168.1.100 TCP_DENIED/403 4295 GET http://askubuntu.com/tags - NONE/- text/html
#
新格式 192.168.1.100 [21/Feb/2013:13:29:45 +0800] 200 13813
TCP_MISS:DIRECT GET
"http://common.cnblogs.com/editor/tiny_mce/plugins/insertCode/images/insertCode.gif"
image/gif
#
# Add any of your own refresh_pattern entries above these.
refresh_pattern ^ftp: 1440 20% 10080
refresh_pattern ^gopher: 1440 0% 1440
refresh_pattern -i (/cgi-bin/|\?) 0 0% 0
refresh_pattern (Release|Packages(.gz)*)$ 0 20% 2880
# example lin deb packages
#refresh_pattern (\.deb|\.udeb)$ 129600 100% 129600
refresh_pattern . 0 20% 4320
内网Firefox设置代理 192.168.1.1:3128 上网正常！
三、PPPOE
1、安装、设置
$ sudo apt-get install pppoe
撤掉宽带路由器，宽带猫直接连到eth0。
$ sudo pppoeconf
进入向导安装模式，基本都是回答yes，尤其是开机自动连接，再填上宽带用户名和密码，ADSL连接就设好了。手动管理ADSL指令如下：
$ ifconfig ppp0 #查看ADSL连接状态
$ sudo pon dsl-provider #手动连接ADSL
$ sudo poff #手动断开ADSL
$ sudo plog #查看ADSL连接日志，仅显示最后一次连接。
2、DNS
DNS设置在 pppoeconf向导中可以设置为从ISP获得，如果喜欢设置自己的DNS，则
$ sudo vi /etc/resolv.conf
nameserver 8.8.8.8
3、网络接口，注：auto dsl-provider开始的内容是pppoeconf向导添加的：
$ cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface
auto lo
iface lo inet loopback
auto eth1
iface eth1 inet static
address 192.168.1.1
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
# gateway 192.168.1.254
dns-nameservers 8.8.8.8
dnd-search domain.com
auto dsl-provider
iface dsl-provider inet ppp
pre-up /sbin/ifconfig eth0 up # line maintained by pppoeconf
provider dsl-provider
auto eth0
iface eth0 inet manual
4、ADSL断线自动重拨，找到/etc/ppp/options 文件里如下几行
# Do not exit after a connection is terminated; instead try to reopen
# the connection.
# persist
去掉 # persist 之前的"# "，试试断开ADSL、重启网络、拔掉ADSL网线片刻再插上等操作，ADSL会在不久之后重新连接，这个时间么，，，有点儿长。
四、Iptables
Ubuntu安装了 iptables，但默认没有启动iptables，也不像 RHEL/Centos 那样把iptables设置为服务。从Centos里复制出来一份 iptables 配置文件，按照自己的需要修改成如下内容：
# Copied from Centos6
# Firewall configuration written by system-config-firewall
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m state -s 192.168.1.0/24 --state NEW -m tcp -p tcp --dport 22 -j ACCEPT #仅允许内网连接ssh
-A INPUT -m state -s 192.168.1.0/24 --state NEW -m tcp -p tcp --dport 3128 -j ACCEPT #仅允许内网连接代理服务
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT
编辑网络配置文件, 在相应网卡的配置文件里增加一句
pre-up iptables-restore /etc/iptables
我的配置如下：
$ sudo vi /etc/network/interfaces
auto dsl-provider
iface dsl-provider inet ppp
pre-up /sbin/ifconfig eth0 up # line maintained by pppoeconf
pre-up iptables-restore /etc/iptables
provider dsl-provider
重启网络
$ sudo /etc/init.d/networking restart
用nmap测试：
配置iptables之前
Nmap scan report for 113.227.36.81
Host is up (0.25s latency).
Not shown: 992 closed ports
PORT STATE SERVICE
22/tcp open ssh
135/tcp filtered msrpc
139/tcp filtered netbios-ssn
445/tcp filtered microsoft-ds
593/tcp filtered http-rpc-epmap
1025/tcp filtered NFS-or-IIS
1434/tcp filtered ms-sql-m
4444/tcp filtered krb524
之后
Nmap scan report for 113.227.56.137
Host is up (0.48s latency).
Not shown: 999 filtered ports
PORT STATE SERVICE
113/tcp closed auth
Nmap scan report for 192.168.1.1
Host is up (0.00022s latency).
Not shown: 998 filtered ports
PORT STATE SERVICE
22/tcp open ssh
3128/tcp open squid-http
内网Firefox设置代理 192.168.1.1:3128 上网正常！
下一步要试试透明代理～～～～～
参考：
http://moko39848381.blog.163.com/blog/static/139827331201012613845110/
http://www.linuxidc.com/Linux/2010-04/25301.htm
以及百度、Bing、Google