centos ADSL 拨号上网设置
下面主要介绍一下，在CentOS命令行环境下如何配置 ADSL 联网：
1、确保安装了网卡并能正常运行，使用命令查看一下网卡状态：
[root@localhost simon]# /sbin/ifconfig eth0
2、在系统中不要设置默认路由(网关)，让 ADSL 拨号后自动获得。
3、查看是否安装了 pppoe 软件包。
[root@localhost simon]# rpm -qa|grep ppp0e
没有显示，说明没有安装，系统光盘里会有这个安装包，或去下载一个 rpm 包，安装一下就OK了。
如下图所示进行安装：
4、安装好软件包后，就可开始配置 ppp0e 客户端软件了，我们不必手工去改动配置文件，可以使用 adsl-setup 这个工具进行配置：
[root@localhost simon]# adsl-setup
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): ***** //（输入 ADSL 帐号的用户名，这里是你去办理宽带时申请的用户名）
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): //（选择网络设备，敲回车，系统就会默认选择）
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): no //（问你是否按需拨号，还是持续连接网络，我选择 no）
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: server //（选择 DNS ，这表示使用 ADSL 拨号会自动获得的 DNS 服务器IP 地址，自动获取就输入 server 吧）
PASSWORD
Please enter your Password: // （输入申请 ADSL 帐号时设置的密码）
Please re-enter your Password:
Sorry, the passwords do not match. Try again? (y/n)y // （我密码输入不匹配，就提示重新输入）
PASSWORD
Please enter your Password: // （输入申请 ADSL 帐号时设置的密码，一定要输入正确哟）
Please re-enter your Password:
USERCTRL
Please enter 'yes' (three letters, lower-case.) if you want to allow
normal user to start or stop DSL connection (default yes): no //（是否允许普通用户启动、关闭）
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): 0 //（选择 firewall 的规则，我选择 0 ，不使用防火墙 ）
Start this connection at boot time
Do you want to start this connection at boot time?
Please enter no or yes (default no):yes // （问你是否选择随机启动）
** Summary of what you entered **
Ethernet Interface: eth0
User name: adsladmin
Activate-on-demand: No
DNS addresses: Supplied by ISP's server
Firewalling: NONE
User Control: no
Accept these settings and adjust configuration files (y/n)? y // （确认一下是否接受设置，如果输入的信息正确，当然选 y 了）
Adjusting /etc/sysconfig/network-scripts/ifcfg-ppp0
Adjusting /etc/ppp/chap-secrets and /etc/ppp/pap-secrets
(But first backing it up to /etc/ppp/chap-secrets.bak)
(But first backing it up to /etc/ppp/pap-secrets.bak)
Congratulations, it should be all set up!
Type '/sbin/ifup ppp0' to bring up your xDSL link and '/sbin/ifdown ppp0'
to bring it down.
Type '/sbin/adsl-status /etc/sysconfig/network-scripts/ifcfg-ppp0'
to see the link status.
[root@localhost simon]# adsl-start // 这里就不用解释了吧
大功告成，开始上网喽
