看看这篇文章吧,我前日子刚用过的.我也是菜鸟,希望能够帮到你.
RedHat 8.0提供ADSL共享上网的解决办法
（转贴一张，我单位用的是铁通的ADSL，以前是固定IP，可后来改为动态的以后就不能用LINUX上了。特转此贴）
一、操作环境：
机器系统与配置：三台机器的关健部件
第一台：台式机，双网卡，8139和8029，操作系统RedHat 8.0
第二台：Toshiba notebook，PC卡。RTL-8139/8139C/8139C+，操作系统RedHat 8.0
第三台：台式机,8029网卡，操作系统windowme
Hub[集线器]：Tp-Link 10M，8口
ADSL，乙太口，非路由。
二、网卡设置如下：
在第一台机器的双网卡的接法：把ADSL接在eth0上，把eth1接在HUB上。
第一块网卡的ip设置：
ip地址:192.168.0.1
掩码:255.255.255.0
第二块网卡的设置
ip地址:192.168.0.2
掩码：255.255.255.0
在这两块网卡中，不要设置网关。
++++++++++++++++++++++++++++++++++++++++
第二台：Toshiba notebook的网卡设置
IP：192.168.0.6
掩码：255.255.255.0
网关：192.168.0.1
DNS:设置电信给的，或者下面的也行
202.96.134.133
202.96.168.68
++++++++++++++++++++++++++++++++++++++++
第三台机器的网卡设置
P：192.168.0.8
掩码：255.255.255.0
网关：192.168.0.1
DNS:设置电信给的，或者下面的也行
202.96.134.133
202.96.168.68
三、设置ppp拔号，
1]删除原来的ppp的ADSL链接。
如果redhat-config-network原来已经用 redhat-config-network设置的ppp的ADSL连接拔号，用下面的命令调用删除。
#redhat-config-network
2]在终端上以root权限运行
#adsl-setup
进入设置过程：
Welcome to the ADSL 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): ADSL提供商给的用户名，写在这里
INTERFACE
Enter the Ethernet interface connected to the ADSL 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): eth0这是ADSL通过第一台机器的第一张网卡eth0提供上网
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):在这里按一下回车就行了。
DNS
Please enter the IP address of your ISPs 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: 202.96.134.133这是DSN，最好用你本地电信给的
Please enter the IP address of your ISPs secondary DNS server.
If you just press enter, I will assume there is only one DNS server.
Enter the secondary DNS server address here: 202.96.168.68这是第二个DNS，也是电信给的。
PASSWORD
Please enter your Password:在这里把ADSL提供商给的密码写上
Please re-enter your Password:
USERCTRL
Please enter yes (two letters, lower-case.) if you want to allow
normal user to start or stop DSL connection (default yes): yes
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): 2
Start this connection at boot time
Do you want to start this connection at boot time?
Please enter no or yes (default no):yes
** Summary of what you entered **
Ethernet Interface: eth0
User name: ADSL用户名
Activate-on-demand: No
Primary DNS: 202.96.134.133
Secondary DNS: 202.96.168.68
Firewalling: MASQUERADE
User Control: yes
Accept these settings and adjust configuration files (y/n)?y
三、在/etc/rc.d/rc.local中加入如下：
echo 1 >; /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -o ppp0 -j MASQUERADE
四、重新启动机器。就OK了。
