Linux 策略路由

1.添加网卡
插入网卡，启动机器，修改/etc/modules.conf并加入
alias eth2 driver.o
2.配置adsl拨号
通过adsl-setup程序创建ppp0和ppp1的拨号配置文件，并保存配置。
修改/etc/sysconfig/network-script/ifcfg-ppp*文件，将其中的PIDFILE参数设为：
PIDFILE=/var/run/ppp-adsl*.pid
其中*对应0、1等
如果不修改此参数将无法启动第二个ppp接口。

3.启动ppp接口
因为adsl-start 命令缺省只能启动第一的ppp接口。所以要启动两个接口，必须指定配置文件。
adsl-start /etc/sysconfig/network-script/ifcfg-ppp0
adsl-start /etc/sysconfig/network-script/ifcfg-ppp1

4.添加路由表
缺省情况下，系统只有3个路由表，local、main、default，路由规则为所有进入的数据报都参照main、defaul来决策路由，这可以通过ip rule ls来查看。其输出如下：
代码:
[root@linuxrouter root]# ip rule ls
0: from all lookup local
32766: from all lookup main
32767: from all lookup 253
[root@linuxrouter root]#

要实现策略路由，添加额外的路由表是必须的。
下面两条命令分别添加名为ppp0和ppp1的路由表。

echo 201 ppp0 >> /etc/iproutes/rt_tables
echo 202 ppp1 >> /etc/iproutes/rt_tables

5.创建路由表项
上面创建的两个路由表都是空表，需要在其中注入路由表项。
本人编写了如下脚本用于注入路由表项：

代码:
#!/bin/bash
# Name: cprt
# This program copy the route from $1 route table to $2 route table,
# exclude the default route entry.

if [ -z "$1" -o -z "$2" ]; then
echo $"usage: cprt <source_table> <dest_table>"
exit 1
fi

SOURCE=$1
DEST=$2

# Clear the destination route table
echo $"Clearing route table $DEST ......"
echo
/sbin/ip route flush table $DEST

# Inject routes from source to destination
echo $"Injecting route from $SOURCE to $DEST ......"
/sbin/ip route ls table $SOURCE | grep -v default > /tmp/route-tmp
while read line; do
/sbin/ip route add table $DEST $line
done < "/tmp/route-tmp"

把main表中的路由表项复制到ppp0和ppp1中。
将下面命令加入到/etc/rc.d/rc.local中。
cprt main ppp0
cprt main ppp1

此 时，两个路由表中都有相同的路由表项了，除了default路由以外。缺省路由的添加要通过另外的途径添加。当ppp激活，或者掉线时，pppd守护进程 会调用/etc/ppp/目录下的ip-up、ip-down脚本，这些教本又分别调用ip-up.local、ip-down.local。在此我们利 用这两个脚本来对路由表和流量控制策略进行维护，此脚本需要人工创建。

下面时本例中的脚本：
代码:
#!/bin/bash
# Name: ip-up.local
# Created by lyking@CU
check_default_route ()
{
LC_ALL=C ip route list table $1 match 0/0 | grep -q default
}

# Determin device here
# We should use IFNAME as the interface name.For some reason, the IFNAME maybe not
# same as the LINKNAME. And the route table should associate with the IFNAME. For
# some conveniency, I name the route table as "ppp0" and "ppp1".
RT_TABLE=$IFNAME

# Add or change static route here
if [ ! `check_default_route $RT_TABLE` ] ; then
ip route change default dev $IFNAME table $RT_TABLE
else
ip route add default dev $IFNAME table $RT_TABLE
fi

# Write some messages for later trubleshooting.
echo >> /var/log/ifchang.log
echo "$0: $IFNAME going up at `date`." >> /var/log/ifchang.log
echo "$0: $IFNAME got address: $IPLOCAL, peer address is $IPREMOTE." >> /var/log/ifchang.log
echo "$0: Table $RT_TABLE default route change to `ip route ls table $RT_TABLE | grep

default`." >> /var/log/ifchang.log

# Refresh routing cache to activating the routing immediately.
ip route flush cache

代码:
#!/bin/bash
# Name: ip-down.local
# Created by lyking@CU
cd /etc/sysconfig/network-scripts
. network-functions

# Determin device here
# We should use IFNAME as the interface name.For some reason, the IFNAME maybe not
# same as the LINKNAME. And the route table should associate with the IFNAME. For
# some conveniency, I name the route table as "ppp0" and "ppp1".
RT_TABLE=$IFNAME
PPPS="ppp0 ppp1"

# Looking for a valide connection to Internet
DEFAULT_RT=""
for i in $PPPS ; do
echo "Checking $i ..." >> /tmp/if-down.log
if [ ! `is_available $i` ] ; then
echo "$i is available." >> /tmp/if-down.log
DEFAULT_RT=$i
break
fi
done

# Update default route here
if [ $DEFAULT_RT != "" ] ; then
ip route add default dev $DEFAULT_RT table $RT_TABLE
else
ip route del default dev $IFNAME table $RT_TABLE
fi

# Write some messages for later trubleshooting.
echo >> /var/log/ifchang.log
echo "$0: $IFNAME going down at `date`." >> /var/log/ifchang.log
echo "$0: Connection lasted $CONNECT_TIME seconds." >> /var/log/ifchang.log
echo "$0: $BYTES_SENT bytes sent, $BYTES_RCVD bytes received." >> /var/log/ifchang.log
echo "$0: Table $RT_TABLE default route changed to `ip route ls table $RT_TABLE | grep

default`. " >> /var/log/ifchang.log

# Refresh routing cache to activating the routing immediately.
ip route flush cache

注意，创建完脚本后必须将其属性改为可执行，否则不会被执行。

6.路由策略的选择
策略路由可以通过源地址、目标地址、ToS或者fwmark标记来进行选择。在此，为了利用iptables的强大的过滤功能采用fwmark标记来决策路由。
在/etc/rc.d/rc.local中添加如下命令：
/sbin/ip rule add fwmark 1 table ppp0
/sbin/ip rule add fwmark 2 table ppp1

7.防火墙规则的添加
这里利用的iptables的强大过滤功能来对流量进行标记。本例中仅根据ip地址的奇偶性来拆分流量，根据具体需求，你还可以根据第4层端口号、ToS等来拆分流量。防火墙需要添加如下命令：

代码:
# Divid traffic to different mark
iptables -t mangle -A PREROUTING -s 10.0.0.0/255.255.255.1 -j MARK --set-mark 0x1
iptables -t mangle -A PREROUTING -s 10.0.0.1/255.255.255.1 -j MARK --set-mark 0x2

# NAT
/sbin/iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
/sbin/iptables -t nat -A POSTROUTING -o ppp1 -j MASQUERADE

至此，双adsl链路的热互备及负载分担基本完成。