http://www.centoscn.com/CentosServer/test/2015/0217/4729.html
环境及要求
内网工作机10台，全为win7系统，网段是192.168.1./24，服务器1台，CentOS6系统(双网卡)。路由器一个（动态IP，通过PPPOP帐户密码上网），48口交换机一个。要求部署CentOS服务器，使其成为代理服务器，内网工作机必须通过服务器链接网络。
分析：成为代理服务器，即CentOS服务器一块网卡成为所有工作组的网关并，另外一块网卡连接外网，然后转发即可。由于是PPPOP拨号上网，还需配置CentOS拨号上网设置。
部署CENTOS6拨号上网
首先是安装拨号程序：
yum -y install rp-pppoe*
然后设置拨号上网：
/usr/sbin/pppop-setupWelcome to the PPPoE client setup. First,I will run some checks on
your system to make sure the PPPoE client is installed properly…LOGIN NAME
Enter your Login Name (default root): #PPPOP的用户名
INTERFACE
Enter the Ethernet interface connected to the PPPoE modem
For Solaris,this is likely to be something like /dev/hme0.
For Linux,it will be ethX,where ‘X’ is a number.
(default eth0): #使用哪块网卡Do you want the link to come up on demand,or stay up continuously?
If you want it to come up on demand,enter the idle time in seconds
after which the link should be dropped. If you want the link to
stay up permanently,enter ‘no’ (two letters,lower-case.)
NOTE: Demand-activated links do not interact well with dynamic IP
addresses.You may have some problems with demand-activated links.
Enter the demand value (default no): #直接回车DNS
Please enter the IP address of your ISP’s primary DNS server.
If your ISP claims that ‘the server will provide dynamic DNS addresses’,
enter ’server’ (all lower-case) here.
If you just press enter,I will assume you kNow what you are
doing and not modify your DNS setup.
Enter the DNS information here: #输入DNSPASSWORD
Please enter your Password: #输入ADSL密码
Please re-enter your Password: #再次输入密码USERCTRL
Please enter ‘yes’ (three letters,lower-case.) if you want to allow
normal user to start or stop DSL connection (default yes): #是否允许普通用户启动连接FIREWALLING
Please choose the firewall rules to use. Note that these rules are
very basic. You are strongly encouraged to use a more sophisticated
firewall setup; however,these will provide basic security. If you
are running any servers on your machine,you must choose ‘NONE’ and
set up firewalling yourself. Otherwise,the firewall rules will deny
access to all standard servers like Web,e-mail,ftp,etc. If you
are using SSH,the rules will block outgoing SSH connections which
allocate a privileged source port.The firewall choices are:
0 – NONE: This script will not set any firewall rules. You are responsible
for ensuring the security of your machine. You are STRONGLY
recommended to use some kind of firewall rules.
1 – STANDALONE: Appropriate for a basic stand-alone web-surfing workstation
2 – MASQUERADE: Appropriate for a machine acting as an Internet gateway
for a LAN
Choose a type of firewall (0-2): #防火墙选择，选择0Start this connection at boot time
Do you want to start this connection at boot time?
Please enter no or yes (default no): #是否自启动** Summary of what you entered **
Ethernet Interface: eth0
User name: root
Activate-on-demand: No
DNS: Do not adjust
Firewalling: NONE
User Control: yes
Accept these settings and adjust configuration files (y/n)? #是否将配置写入配置文件，输入y
之后就可以启动ADSL进行拨号上网了：
/usr/sbin/pppoe-start
如果没有连接上，请检查下配置文件是否正确，网线是否插好等。将其加入到开机启动项：
chkconfig pppoe-server on
设置CENTOS服务器内网转发
部署另外一块网卡IP配置信息，假定ADSL使用了eth0网卡，ip为202.102.123.32，内网使用eth1网卡，IP为192.168.1.1（/etc/sysconfig/network-scripts/ifcfg-eth1设置为静态）.
开启IP转发
echo 1 >/proc/sys/net/ipv4/ip_forward
配置iptables规则
iptables -t nat -A POSTROUTING -j MASQUERADE
iptables -t nat -A POSTROUTING –s 192.168.1.0/24 -j MASQUERADE
配置静态路由规则
route add -net 202.102.123.32 netmask 255.255.255.0
route add -net 192.168.1.1 netmask 255.255.255.0
route add default gw 202.102.123.32
设置开机自动启动
vim /etc/rc.local
/sbin/iptables -t nat -A POSTROUTING –s 192.168.1.0/24 -j MASQUERADE
echo 1 >/proc/sys/net/ipv4/ip_forward
设置工作机上网
将工作机的网关设置为192.168.1.1即可通过CentOS服务器上网了。
