纯手工打造linux路由器

对由器比较了解的朋友都知道，很多专业级的路由器，也就是用linux系统来做的，那既然如此，如何使用linux主机打造一个路由器了。其实也不难，但我们得首先搞楚路由器的工作原理，说白了路由器也就是两个不同的网络之间转发数据之用的。如果没有路由器，只能在各自的网络内互相通信，跨网络就访问不了了。因为它们之间是相互隔离的，必须要有一个桥梁才能让它们之间正常来往。今天就给大家分享如何使用两台linux主机来打造一台路由器。

一、环境需求
1、两台双网卡主机
2、操作系统：安装Centos7.2

二、路由要求：实现A网络和B网络的通信
A网络：192.168.1.0/24
B网络：192.168.2.0/24
路由器的网络：192.168.0.0/24

三、配置思路
第一台linux主机（R1）：
第一块网卡——A网络的网关（内网接口）：192.168.1.254
第二块网卡——A网络的出口（外网接口）：192.168.0.1

第二台linux主机（R2）：
第一块网卡——B网络的网关（内网接口）：192.168.2.254
第二块网卡——B网络的出口（外网接口）：192.168.0.2



四、具体配置步骤
第一步：配置两台主机的网卡（每台主机两张网卡，需要配置四次）
（一）R1的网卡配置
[root@Router1 network-scripts]# ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eno16777728: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
link/ether 00:0c:29:13:4b:5f brd ff:ff:ff:ff:ff:ff
3: eno33554960: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
link/ether 00:0c:29:13:4b:69 brd ff:ff:ff:ff:ff:ff
4: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT
link/ether 52:54:00:3a:39:12 brd ff:ff:ff:ff:ff:ff
5: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast master virbr0 state DOWN mode DEFAULT qlen 500
link/ether 52:54:00:3a:39:12 brd ff:ff:ff:ff:ff:ff
[root@Router1 network-scripts]# vim ifcfg-eno16777728
[root@Router1 network-scripts]# cat ifcfg-eno16777728
DEVICE=eno16777728
BOOTPROTO=none
IPADDR=192.168.1.254
PREFIX=24
[root@Router1 network-scripts]# vim ifcfg-eno33554960
[root@Router1 network-scripts]# cat ifcfg-eno33554960
DEVICE=eno33554960
BOOTPROTO=none
IPADDR=192.168.0.1
PREFIX=24
[root@Router1 network-scripts]#

（二）R2的网卡配置
[root@Router2 network-scripts]# ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eno16777728: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
link/ether 00:0c:29:6f:d4:c5 brd ff:ff:ff:ff:ff:ff
3: eno33554960: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
link/ether 00:0c:29:6f:d4:cf brd ff:ff:ff:ff:ff:ff
4: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT
link/ether 52:54:00:3a:39:12 brd ff:ff:ff:ff:ff:ff
5: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast master virbr0 state DOWN mode DEFAULT qlen 500
link/ether 52:54:00:3a:39:12 brd ff:ff:ff:ff:ff:ff
[root@Router2 network-scripts]# vim ifcfg-eno16777728
[root@Router2 network-scripts]# cat ifcfg-eno16777728
DEVICE=eno16777728
BOOTPROTO=none
IPADDR=192.168.2.254
PREFIX=24
[root@Router2 network-scripts]# vim ifcfg-eno33554960
[root@Router2 network-scripts]# cat ifcfg-eno33554960
DEVICE=eno33554960
BOOTPROTO=none
IPADDR=192.168.0.2
PREFIX=24
[root@Router2 network-scripts]#

第二步：配置两台主机的路由表
（一）R1的路由表配置
[root@Router1 network-scripts]# echo "192.168.2.0/24 via 192.168.0.2" > route-eno33554960
[root@Router1 network-scripts]# cat route-eno33554960
192.168.2.0/24 via 192.168.0.2
[root@Router1 network-scripts]#

（二）R2的路由表配置
[root@Router2 network-scripts]# echo "192.168.1.0/24 via 192.168.0.1" > route-eno33554960
[root@Router2 network-scripts]# cat route-eno33554960
192.168.1.0/24 via 192.168.0.1
[root@Router2 network-scripts]#

第三步：开启两台主机的路由转发功能
（一）开启R1的路由转发功能
[root@Router1 network-scripts]# cat /proc/sys/net/ipv4/ip_forward
0
[root@Router1 network-scripts]# echo 1 > /proc/sys/net/ipv4/ip_forward
[root@Router1 network-scripts]#

（二）开启R2的路由转发功能
[root@Router2 network-scripts]# cat /proc/sys/net/ipv4/ip_forward
0
[root@Router2 network-scripts]# echo 1 > /proc/sys/net/ipv4/ip_forward
[root@Router2 network-scripts]#

第四步：重启两台已经配置好的路由器，并验证两台路由器之间的通信
（一）重启R1
[root@Router1 network-scripts]# systemctl restart network
[root@Router1 network-scripts]# ifconfig
eno16777728: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.1.254 netmask 255.255.255.0 broadcast 192.168.1.255
inet6 fe80::20c:29ff:fe13:4b5f prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:13:4b:5f txqueuelen 1000 (Ethernet)
RX packets 21778 bytes 1755783 (1.6 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 1569 bytes 206822 (201.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

eno33554960: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.0.1 netmask 255.255.255.0 broadcast 192.168.0.255
inet6 fe80::20c:29ff:fe13:4b69 prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:13:4b:69 txqueuelen 1000 (Ethernet)
RX packets 19431 bytes 1527793 (1.4 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 94 bytes 10757 (10.5 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 0 (Local Loopback)
RX packets 8 bytes 688 (688.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 8 bytes 688 (688.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

virbr0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
inet 192.168.122.1 netmask 255.255.255.0 broadcast 192.168.122.255
ether 52:54:00:3a:39:12 txqueuelen 0 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

[root@Router1 network-scripts]#

（二）重启R2
[root@Router2 network-scripts]# systemctl restart network
[root@Router2 network-scripts]# ifconfig
eno16777728: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.2.254 netmask 255.255.255.0 broadcast 192.168.2.255
inet6 fe80::20c:29ff:fe6f:d4c5 prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:6f:d4:c5 txqueuelen 1000 (Ethernet)
RX packets 20833 bytes 1658328 (1.5 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 1372 bytes 217031 (211.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

eno33554960: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.0.2 netmask 255.255.255.0 broadcast 192.168.0.255
inet6 fe80::20c:29ff:fe6f:d4cf prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:6f:d4:cf txqueuelen 1000 (Ethernet)
RX packets 18938 bytes 1480549 (1.4 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 81 bytes 9518 (9.2 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 0 (Local Loopback)
RX packets 8 bytes 688 (688.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 8 bytes 688 (688.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

virbr0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
inet 192.168.122.1 netmask 255.255.255.0 broadcast 192.168.122.255
ether 52:54:00:3a:39:12 txqueuelen 0 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

[root@Router2 network-scripts]#

（三）用R1 ping R2
[root@Router1 network-scripts]# ping -c3 192.168.0.2
PING 192.168.0.2 (192.168.0.2) 56(84) bytes of data.
64 bytes from 192.168.0.2: icmp_seq=1 ttl=64 time=15.4 ms
64 bytes from 192.168.0.2: icmp_seq=2 ttl=64 time=1.23 ms
64 bytes from 192.168.0.2: icmp_seq=3 ttl=64 time=1.31 ms

--- 192.168.0.2 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2018ms
rtt min/avg/max/mdev = 1.238/6.003/15.453/6.682 ms
[root@Router1 network-scripts]# ping -c3 192.168.2.254
PING 192.168.2.254 (192.168.2.254) 56(84) bytes of data.
64 bytes from 192.168.2.254: icmp_seq=1 ttl=64 time=0.912 ms
64 bytes from 192.168.2.254: icmp_seq=2 ttl=64 time=1.27 ms
64 bytes from 192.168.2.254: icmp_seq=3 ttl=64 time=1.90 ms

--- 192.168.2.254 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2022ms
rtt min/avg/max/mdev = 0.912/1.364/1.903/0.409 ms
[root@Router1 network-scripts]#

（四）用R2 ping R1
[root@Router2 network-scripts]# ping -c3 192.168.0.1
PING 192.168.0.1 (192.168.0.1) 56(84) bytes of data.
64 bytes from 192.168.0.1: icmp_seq=1 ttl=64 time=0.572 ms
64 bytes from 192.168.0.1: icmp_seq=2 ttl=64 time=0.951 ms
64 bytes from 192.168.0.1: icmp_seq=3 ttl=64 time=0.822 ms

--- 192.168.0.1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2029ms
rtt min/avg/max/mdev = 0.572/0.781/0.951/0.160 ms
[root@Router2 network-scripts]# ping -c3 192.168.1.254
PING 192.168.1.254 (192.168.1.254) 56(84) bytes of data.
64 bytes from 192.168.1.254: icmp_seq=1 ttl=64 time=6.78 ms
64 bytes from 192.168.1.254: icmp_seq=2 ttl=64 time=0.962 ms
64 bytes from 192.168.1.254: icmp_seq=3 ttl=64 time=1.14 ms

--- 192.168.1.254 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2026ms
rtt min/avg/max/mdev = 0.962/2.963/6.785/2.703 ms
[root@Router2 network-scripts]#

第五步：配置windows主机做为A网络的PC1，配置另一台liunx主机做为B网络的PC2，分别用测试路由效果
（一）PC1-->A网络的windows7
C:\Users\Administrator>ipconfig

Windows IP 配置
以太网适配器 本地连接:

连接特定的 DNS 后缀 . . . . . . . :
IPv4 地址 . . . . . . . . . . . . : 192.168.1.125
子网掩码 . . . . . . . . . . . . : 255.255.255.0
默认网关. . . . . . . . . . . . . : 192.168.1.254

隧道适配器 isatap.{CCC82E88-7D5E-4564-B569-27B6A5DE9C48}:

媒体状态 . . . . . . . . . . . . : 媒体已断开
连接特定的 DNS 后缀 . . . . . . . :

C:\Users\Administrator>

（二）PC2-->B网络的Centos7.2
[root@centos7 ~]# cat /etc/sysconfig/network-scripts/
cat: /etc/sysconfig/network-scripts/: Is a directory
[root@centos7 ~]# cat /etc/sysconfig/network-scripts/ifcfg-eno16777728
DEVICE=eno16777728
BOOTPROTO=none
IPADDR=192.168.2.125
PREFIX=24
GATEWAY=192.168.2.254
[root@centos7 ~]# ifconfig
eno16777728: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.2.125 netmask 255.255.255.0 broadcast 192.168.2.255
inet6 fe80::20c:29ff:fe06:f987 prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:06:f9:87 txqueuelen 1000 (Ethernet)
RX packets 1359 bytes 98258 (95.9 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 136 bytes 12455 (12.1 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 0 (Local Loopback)
RX packets 16 bytes 1072 (1.0 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 16 bytes 1072 (1.0 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

[root@centos7 ~]#

（三）现在用A网络的PC1（192.168.1.125/24） ping B网络的PC2（192.168.2.125/24）

C:\Users\Administrator>ping 192.168.2.125

正在 Ping 192.168.2.125 具有 32 字节的数据:
来自 192.168.2.125 的回复: 字节=32 时间=1ms TTL=62
来自 192.168.2.125 的回复: 字节=32 时间=2ms TTL=62
来自 192.168.2.125 的回复: 字节=32 时间=3ms TTL=62
来自 192.168.2.125 的回复: 字节=32 时间=2ms TTL=62

192.168.2.125 的 Ping 统计信息:
数据包: 已发送 = 4，已接收 = 4，丢失 = 0 (0% 丢失)，
往返行程的估计时间(以毫秒为单位):
最短 = 1ms，最长 = 3ms，平均 = 2ms

C:\Users\Administrator>
经过两个路由器，所以TTL变成62（64-2）

（四）再用B网络的PC2（192.168.2.125/24）ping A网络的PC1（192.168.1.125/24）
[root@centos7 ~]# ping -c4 192.168.1.125
PING 192.168.1.125 (192.168.1.125) 56(84) bytes of data.
64 bytes from 192.168.1.125: icmp_seq=1 ttl=62 time=1.39 ms
64 bytes from 192.168.1.125: icmp_seq=2 ttl=62 time=1.19 ms
64 bytes from 192.168.1.125: icmp_seq=3 ttl=62 time=2.03 ms
64 bytes from 192.168.1.125: icmp_seq=4 ttl=62 time=2.12 ms

--- 192.168.1.125 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3008ms
rtt min/avg/max/mdev = 1.198/1.689/2.126/0.402 ms
[root@centos7 ~]#
经过两个路由器，所以TTL同样的是62

原本属于两个不同网络的PC1和PC2是不能通信的，现在有了刚才搭建的路由器（R1+R2），它们就可以正常通信了。

传说中的路由器也就是这么工作的，当然这只是给大家展示了一下路由器的工作原理，同时这也只是静态路由的情况，动态路由就比静态路由要复杂的多了。