一．Linux与Linux之间的互拔：
请看图一：
我家里： 办公室：
机器名：j128 机器名：vms68
OS: RedHat5.1 OS: RedHat5.1
IP: 192.168.88.128 <----电话网----> IP: 192.168.89.68 <--->
Internet
| [ttyS0] [ttyS1] [ttyS0]
|网线
|
机器名：j003
OS: Win98
IP: 192.168.88.3
第一步要配置Linux为ppp服务器，允许拔入，如姚飞所说：
使用mgetty
(以下假设modem装在ttyS0)
cd /etc
vi inittab
add :
d1:2345:respawn:/sbin/mgetty ttyS0 # COM1口允许拔入
d2:2345:respawn:/sbin/mgetty ttyS1 # COM2口允许拔入
then: init q # 重读配置文件/etc/inittab
注意, 如果想拔号出去, pppd 使用的设备也必须是/dev/ttyS0或/dev/ttyS1,
而不是/dev/modem, 要不然是拨不出去的.
我这样做后，j128和vms68都可允许拔入，但还不是ppp server，还需要以下几步：
在vms68里：
adduser ppp #新加一个用户
passwd ppp #为ppp起个密码
在/home/ppp下建一个脚本ppplogin，内容如下：
exec /usr/sbin/pppd 115200 modem asyncmap 0 proxyarp \
192.168.89.68:192.193.89.69
##### LOCALIP:REMOTEIP
vi /etc/passwd
将这行ppp:xxxx:505:505:ppp acount:/home/ppp:/bin/bash
改为ppp:xxxx:505:505:ppp acount:/home/ppp:/home/ppp/ppplogin
在j128里：
adduser ppp #新加一个用户
passwd ppp #为ppp起个密码
在/home/ppp下建一个脚本ppplogin，内容如下：
exec /usr/sbin/pppd 115200 modem asyncmap 0 proxyarp \
0.0.0.0:0.0.0.0.0 ###等vms68分配ip地址
vi /etc/passwd
将这行ppp:xxxx:505:505:ppp acount:/home/ppp:/bin/bash
改为ppp:xxxx:505:505:ppp acount:/home/ppp:/home/ppp/ppplogin
下一步要配j128拔到vms68，这很简单，
跟拔到Internet是一样的，文件ppp-onvms68如下：
# Script to initiate a ppp connection. This is the first part of the
# pair of scripts. This is not a secure pair of scripts as the codes
# are visible with the ps command. However, it is simple.
#
# These are the parameters. Change as needed.
TELEPHONE=xxxx # The telephone number for the connection
ACCOUNT=ppp # The account name for logon (as in George Burns)
PASSWORD=xxxx # The password for this account (and Gracie Allen)
LOCAL_IP=0.0.0.0 # Local IP address if known. Dynamic = 0.0.0.0
REMOTE_IP=0.0.0.0 # Remote IP address if desired. Normally 0.0.0.0
NETMASK=255.255.255.0 # The proper netmask if needed
#
# Export them so that they will be available at ppp-on-dialer time.
export TELEPHONE ACCOUNT PASSWORD
#
# This is the location of the script which dials the phone and logs
# in. Please use the absolute file name as the $PATH variable is not
# used on the connect option. (To do so on a root account would be
# a security hole so dont ask.)
#
DIALER_SCRIPT=/home/ppp/ppp-on-dialer
#
# Initiate the connection
#
# I put most of the common options on this command. Please, dont
# forget the lock option or some programs such as mgetty will not
# work. The asyncmap and escape will permit the PPP link to work with
# a telnet or rlogin connection. You are welcome to make any changes
# as desired. Dont use the defaultroute option if you currently
# have a default route to an ethernet gateway.
#
exec /usr/sbin/pppd /dev/ttyS0 115200 modem $LOCAL_IP:$REMOTE_IP \
defaultroute lock crtscts asyncmap 0 connect $DIALER_SCRIPT \
debug
现在配vms68拔到j128，文件ppp-onj128如下:
# Script to initiate a ppp connection. This is the first part of the
# pair of scripts. This is not a secure pair of scripts as the codes
# are visible with the ps command. However, it is simple.
#
# These are the parameters. Change as needed.
TELEPHONE=xxxx # The telephone number for the connection
ACCOUNT=ppp # The account name for logon (as in George Burns)
PASSWORD=xxxx # The password for this account (and Gracie Allen)
LOCAL_IP=192.168.89.68 # Local IP address if known. Dynamic = 0.0.0.0
REMOTE_IP=192.168.89.69 # Remote IP address if desired. Normally 0.0.0.0
NETMASK=255.255.255.0 # The proper netmask if needed
#
# Export them so that they will be available at ppp-on-dialer time.
export TELEPHONE ACCOUNT PASSWORD
#
# This is the location of the script which dials the phone and logs
# in. Please use the absolute file name as the $PATH variable is not
# used on the connect option. (To do so on a root account would be
# a security hole so dont ask.)
#
DIALER_SCRIPT=/home/ppp/ppp-on-dialer
#
# Initiate the connection
#
# I put most of the common options on this command. Please, dont
# forget the lock option or some programs such as mgetty will not
# work. The asyncmap and escape will permit the PPP link to work with
# a telnet or rlogin connection. You are welcome to make any changes
# as desired. Dont use the defaultroute option if you currently
# have a default route to an ethernet gateway.
#
exec /usr/sbin/pppd /dev/ttyS1 115200 modem $LOCAL_IP:$REMOTE_IP \
lock crtscts asyncmap 0 connect $DIALER_SCRIPT \
debug
这里要注意LOCAL_IP和REMOTE_IP要给值，还有的是在pppd里没有defaultroute。
因为vms68还要拔上Internet，所以不要defaultroute。
在j128上用ppp-onvms68拔上vms68，连通后telnet vms68，执行以下命令：
nohup sleep 30;ppp-onj128
然后在j128上断线，等待vms68拔入。拔通后，在j128上要执行以下命令：
route add -net 192.168.89.0 gw 192.168.89.69 ppp0
route add default gw 192.168.89.69 ppp0
ipfwadm -F -a m -S 192.168.88.0/24 -D 0.0.0.0/0
现在可再telnet vms68，在vms68上拔号上网，这样j003可通过j128，再通
过vms68上网，我也不用付任何费用。
二．Win98与Linux之间的互拔：
请看图二：
我家里： 办公室：
机器名：j128 机器名：vms68
OS: RedHat5.1 OS: RedHat5.1
IP: 192.168.88.128 IP: 192.168.89.68 <--->
Internet
| [ttyS1] [ttyS0]
|网线 |
| |
机器名：j003 |
OS: Win98 ---------------------------
IP: 192.168.88.3 电话网
这里vms68要象第一步所说的，要配成允许拔入的ppp server。
这里主要是win98的配置，首先象上Internet那样，在拔号网络里新建一个连接，
要注意两点，一要设置连通后弹出终端窗口，二是最主要的，在“控制面板”里
选“调制解调器”，选用来连线的modem，选“属性”按钮，选“连接”，再选
“高级”按钮，再在“附加设置”里输入&C0S0=001。
为什么要这样做？因为win98自带的ppp client会自动退出当远端ppp server挂线
时，因此要骗一骗win98，要modem不要报告断线，并自动应答拔入。&C0就是要
modem不要检测carrier，s0=001要modem在响一下后就应答。
现在配vms68拔到j003，文件ppp-onj003如下:
# Script to initiate a ppp connection. This is the first part of the
# pair of scripts. This is not a secure pair of scripts as the codes
# are visible with the ps command. However, it is simple.
#
# These are the parameters. Change as needed.
TELEPHONE=xxxx # The telephone number for the connection
#ACCOUNT=ppp # The account name for logon (as in George Burns)
#PASSWORD=xxxx # The password for this account (and Gracie Allen)
LOCAL_IP=192.168.89.68 # Local IP address if known. Dynamic = 0.0.0.0
REMOTE_IP=192.168.89.69 # Remote IP address if desired. Normally 0.0.0.0
NETMASK=255.255.255.0 # The proper netmask if needed
#
# Export them so that they will be available at ppp-on-dialer time.
export TELEPHONE ###ACCOUNT PASSWORD
#
# This is the location of the script which dials the phone and logs
# in. Please use the absolute file name as the $PATH variable is not
# used on the connect option. (To do so on a root account would be
# a security hole so dont ask.)
#
DIALER_SCRIPT=/home/ppp/ppp-on-dialer
#
# Initiate the connection
#
# I put most of the common options on this command. Please, dont
# forget the lock option or some programs such as mgetty will not
# work. The asyncmap and escape will permit the PPP link to work with
# a telnet or rlogin connection. You are welcome to make any changes
# as desired. Dont use the defaultroute option if you currently
# have a default route to an ethernet gateway.
#
exec /usr/sbin/pppd /dev/ttyS1 115200 modem $LOCAL_IP:$REMOTE_IP \
lock crtscts asyncmap 0 connect $DIALER_SCRIPT \
debug
这里要注意LOCAL_IP和REMOTE_IP要给值，还有的是在pppd里没有defaultroute。
因为vms68还要拔上Internet，所以不要defaultroute。还有这里没有ACOUNT和
PASSWORD，因为WIN98的PPP CLIENT不要用户名和密码，因此在PPP-ON-DIALER里
要把送ACOUNT和PASSWORD的那两行去掉。
J003通过拔号拔上VMS68后，要TELNET VMS68，在VMS68里执行以下脚本：
kill `cat /var/run/ppp0.pid` ###注意如果是用ppp1，就用ppp1.pid
nohup sleep 30;ppp-onj003
这里要特别注意的一点是一定要在linux里断线，因为在WIN98里断线，则WIN98
的PPP CLIENT就会退出，就不会应答呼叫。
现在WIN98和LINUX之间就可以实现回拔了，但要注意WIN98的路由问题。
在win98下要自配一下路由，在win98的目录里有route程序，它的格式如下：
route print/add/delete/change (直接打route就有帮助看)
象我的j003，在没有拔号时，用route print得到如下信息：(行号是我加上的)
