要求：
eth0：192.168.100.203 连接内网，网关为192.168.100.1。需要和192.168.10.0、192.168.12.0、192.168.100.0、10.2.2.0、10.2.1.0网段通信。
eth1:172.16.0.203 连接外网，网关为172.16.0.254。需要访问外网。
配置思路：
eth1设置默认网关，生成0.0.0.0的默认路由，eth0不设置网关，手动添加静态路由。
[root@dcServer003 ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
# Broadcom Corporation NetXtreme II BCM5709 Gigabit Ethernet
DEVICE=eth0
BOOTPROTO=none
HWADDR=D8:D3::FA::
ONBOOT=yes
IPADDR=192.168.100.203
NETMASK=255.255.255.0
#GATEWAY=192.168.100.1
TYPE=Ethernet
eth0 配置
[root@dcServer003 ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth1
# Broadcom Corporation NetXtreme II BCM5709 Gigabit Ethernet
DEVICE=eth1
BOOTPROTO=static
HWADDR=d8:d3::fa::
ONBOOT=yes
NETMASK=255.255.255.0
IPADDR=172.16.0.203
GATEWAY=172.16.0.254
TYPE=Ethernet
eth1配置
[root@dcServer003 ~]# cat /etc/rc.local
#!/bin/sh
#
# This script will be executed *after* all the other init scripts.
# You can put your own initialization stuff in here if you don't
# want to do the full Sys V style init stuff. touch /var/lock/subsys/local
route add -net 192.168.10.0/ gw 192.168.100.1 eth0
route add -net 192.168.12.0/ gw 192.168.100.1 eth0
route add -net 192.168.100.0/ gw 192.168.100.1 eth0
route add -net 10.2.1.0/ gw 192.168.100.1 eth0
route add -net 10.2.2.0/ gw 192.168.100.1 eth0
[root@dcServer003 ~]# route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.100.0 192.168.100.1 255.255.255.0 UG eth0
192.168.100.0 * 255.255.255.0 U eth0
10.2.1.0 192.168.100.1 255.255.255.0 UG eth0
10.2.2.0 192.168.100.1 255.255.255.0 UG eth0
172.16.0.0 * 255.255.255.0 U eth1
192.168.12.0 192.168.100.1 255.255.255.0 UG eth0
192.168.10.0 192.168.100.1 255.255.255.0 UG eth0
169.254.0.0 * 255.255.0.0 U eth1
default 172.16.0.254 0.0.0.0 UG eth1 [root@dcServer003 ~]# tracert www.baidu.com
traceroute to www.baidu.com (61.135.169.121), hops max, byte packets
172.16.0.254 (172.16.0.254) 0.521 ms 0.518 ms 0.517 ms
100.64.0.1 (100.64.0.1) 3.451 ms 3.524 ms 3.558 ms
111.175.224.53 (111.175.224.53) 3.672 ms 3.686 ms 3.774 ms
111.175.208.229 (111.175.208.229) 8.447 ms 8.430 ms 8.434 ms
(202.97.67.29) 32.737 ms 32.593 ms 32.817 ms
202.97.88.254 (202.97.88.254) 27.398 ms * *
219.158.44.133 (219.158.44.133) 26.144 ms * *
* * *
61.49.214.6 (61.49.214.6) 27.650 ms 27.653 ms 27.715 ms
123.126.6.118 (123.126.6.118) 25.847 ms 25.937 ms 26.910 ms
* 61.49.168.78 (61.49.168.78) 24.593 ms *
61.135.169.121 (61.135.169.121) 26.060 ms 26.112 ms 25.905 ms
[root@dcServer003 ~]# tracert 192.168.10.61
traceroute to 192.168.10.61 (192.168.10.61), hops max, byte packets
192.168.100.2 (192.168.100.2) 3.135 ms 3.112 ms 3.201 ms
192.168.10.61 (192.168.10.61) 0.345 ms 0.351 ms 0.349 ms
实际工作中192.168.100.203上开启了一个squid代理，所以需要开启路由转发：echo 1 > /proc/sys/net/ipv4/ip_forward
设置本地两个网卡能互ping：
iptables -t nat -A POSTROUTING -s 192.168.100.0/24 -d 172.16.0.0/24 -o eth1 -j MASQUERADE
iptables -t nat -A POSTROUTING -s 172.16.0.0/24 -d 192.168.100.0/24 -o eth0 -j MASQUERADE