Linux 配置路由转发功能测试

测试Linux配置路由转发功能。

参考

1. 手把手带你将 Linux 主机配置为静态路由器
2. tcpdump详解&实战

环境

操作系统

Centos7.9

网络环境

1. 三台主机的网卡 enp0s5 均在 10.211.55.0/24 网段，且网络可以通讯

• centos7-18的IP 10.211.55.18，作为路由服务端
• centos7-10的IP 10.211.55.10，作为子网连接端
• centos7-22的IP 10.211.55.22，作为子网连接端

2. 两台子网连接端配置子网IP

• 主机centos7-10 网卡enp0s5配置子网 192.168.10.100/32（子网一个IP）
• 主机centos7-22 网卡enp0s5配置子网 172.16.1.200/32（子网一个IP）

3. 配置子网连接端的静态路由

• 主机centos7-10（192.168.10.100/32），增加访问 172.16.1.200/32 的静态路由
• 主机centos7-22（172.16.1.200/32），增加访问 192.168.10.100/32 的静态路由

4. 开启路由服务端的路由转发功能

• 主机centos7-18（10.211.55.18）， 配置访问 192.168.10.100 和 172.16.1.200的静态路由
• 主机centos7-18（10.211.55.18），开启路由转发功能，实现192.168.10.100/32 与 172.16.1.200/32 之间通讯。

测试步骤

1. 配置主机centos7-10

• 配置子网IP 192.168.10.100

[root@centos7-10 ~]# ip addr add 192.168.10.100 dev enp0s5
[root@centos7-10 ~]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp0s5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:1c:42:ae:b6:41 brd ff:ff:ff:ff:ff:ff
    inet 10.211.55.10/24 brd 10.211.55.255 scope global noprefixroute dynamic enp0s5
       valid_lft 1743sec preferred_lft 1743sec
    inet 192.168.10.100/32 scope global enp0s5
       valid_lft forever preferred_lft forever
    inet6 fdb2:2c26:f4e4:0:cd1f:12f3:4076:6d89/64 scope global noprefixroute dynamic 
       valid_lft 2591943sec preferred_lft 604743sec
    inet6 fe80::7e0c:1902:e1ca:4324/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

• 配置访问 172.16.1.200 的静态路由

[root@centos7-10 ~]# ip route 172.16.1.200 via 10.211.55.18 dev enp0s5
[root@centos7-10 ~]# ip route
default via 10.211.55.1 dev enp0s5 proto dhcp metric 100 
10.211.55.0/24 dev enp0s5 proto kernel scope link src 10.211.55.10 metric 100 
172.16.1.200 via 10.211.55.18 dev enp0s5 
192.168.10.100 dev enp0s5 proto kernel scope link src 192.168.10.100 metric 100 
[root@centos7-10 ~]# 

2. 配置主机centos7-22

• 配置子网IP 172.16.1.200

[root@centos7-22 ~]# ip addr add 172.16.1.200 dev enp0s5
[root@centos7-22 ~]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp0s5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:1c:42:44:79:a5 brd ff:ff:ff:ff:ff:ff
    inet 10.211.55.22/24 brd 10.211.55.255 scope global noprefixroute dynamic enp0s5
       valid_lft 1605sec preferred_lft 1605sec
    inet 172.16.1.200/32 scope global enp0s5
       valid_lft forever preferred_lft forever
    inet6 fdb2:2c26:f4e4:0:233e:38df:2cbd:cec1/64 scope global noprefixroute dynamic 
       valid_lft 2591809sec preferred_lft 604609sec
    inet6 fe80::7e0c:1902:e1ca:4324/64 scope link tentative noprefixroute dadfailed 
       valid_lft forever preferred_lft forever
    inet6 fe80::567a:248b:5e94:5d19/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

• 配置访问 192.168.10.100 的静态路由

[root@centos7-22 ~]# ip route add 192.168.10.100 via 10.211.55.18 dev enp0s5
[root@centos7-22 ~]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp0s5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:1c:42:44:79:a5 brd ff:ff:ff:ff:ff:ff
    inet 10.211.55.22/24 brd 10.211.55.255 scope global noprefixroute dynamic enp0s5
       valid_lft 1565sec preferred_lft 1565sec
    inet 172.16.1.200/32 scope global enp0s5
       valid_lft forever preferred_lft forever
    inet6 fdb2:2c26:f4e4:0:233e:38df:2cbd:cec1/64 scope global noprefixroute dynamic 
       valid_lft 2591768sec preferred_lft 604568sec
    inet6 fe80::7e0c:1902:e1ca:4324/64 scope link tentative noprefixroute dadfailed 
       valid_lft forever preferred_lft forever
    inet6 fe80::567a:248b:5e94:5d19/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

3. 配置主机centos7-18

• 配置访问 192.168.10.100 和 172.16.1.200 的静态路由

[root@centos7-18 ~]# ip route add 192.168.10.100 via 10.211.55.10 dev enp0s5
[root@centos7-18 ~]# ip route add 172.16.1.200 via 10.211.55.22 dev enp0s5
[root@centos7-18 ~]# ip route
default via 10.211.55.1 dev enp0s5 
10.211.55.0/24 dev enp0s5 proto kernel scope link src 10.211.55.18 
172.16.1.200 via 10.211.55.22 dev enp0s5 
192.168.10.100 via 10.211.55.10 dev enp0s5 

// 查看主机centos7-18的IP配置
[root@centos7-18 ~]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp0s5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:1c:42:60:87:b2 brd ff:ff:ff:ff:ff:ff
    inet 10.211.55.18/24 brd 10.211.55.255 scope global enp0s5
       valid_lft forever preferred_lft forever
    inet6 fdb2:2c26:f4e4:0:21c:42ff:fe60:87b2/64 scope global mngtmpaddr dynamic 
       valid_lft 2591430sec preferred_lft 604230sec
    inet6 fe80::21c:42ff:fe60:87b2/64 scope link 
       valid_lft forever preferred_lft forever

4. 路由转发测试

4.1 关闭路由转发测试

• centos7-18设置 net.ipv4.ip_forward = 0，关闭路由转发功能
• centos7-10测试 Ping 172.16.1.200，网络不通

// 设置 net.ipv4.ip_forward = 0，关闭路由转发功能
[root@centos7-18 ~]# sysctl -w net.ipv4.ip_forward=0
net.ipv4.ip_forward = 0

// 测试 192.168.10.100 Ping 172.16.1.200，网络不通
[root@centos7-10 ~]# ping 172.16.1.200 -c5
PING 172.16.1.200 (172.16.1.200) 56(84) bytes of data.

--- 172.16.1.200 ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 4017ms

[root@centos7-10 ~]# 

4.2 开启路由转发测试

• centos7-18设置 net.ipv4.ip_forward = 1，开启路由转发功能
• centos7-10测试 Ping 172.16.1.200，网络通

// 设置 net.ipv4.ip_forward = 1，开启路由转发功能
[root@centos7-18 ~]# sysctl -w net.ipv4.ip_forward=1
net.ipv4.ip_forward = 1

// 测试 192.168.10.100 Ping 172.16.1.200，网络通
[root@centos7-10 ~]# ping 172.16.1.200 -c5
PING 172.16.1.200 (172.16.1.200) 56(84) bytes of data.
64 bytes from 172.16.1.200: icmp_seq=1 ttl=64 time=0.850 ms
From 10.211.55.18: icmp_seq=2 Redirect Host(New nexthop: 10.211.55.22)
64 bytes from 172.16.1.200: icmp_seq=2 ttl=64 time=0.752 ms
From 10.211.55.18: icmp_seq=3 Redirect Host(New nexthop: 10.211.55.22)
64 bytes from 172.16.1.200: icmp_seq=3 ttl=64 time=0.729 ms
From 10.211.55.18: icmp_seq=4 Redirect Host(New nexthop: 10.211.55.22)
64 bytes from 172.16.1.200: icmp_seq=4 ttl=64 time=0.471 ms
From 10.211.55.18: icmp_seq=5 Redirect Host(New nexthop: 10.211.55.22)
64 bytes from 172.16.1.200: icmp_seq=5 ttl=64 time=0.779 ms

--- 172.16.1.200 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4011ms
rtt min/avg/max/mdev = 0.471/0.716/0.850/0.130 ms
[root@centos7-10 ~]# 

• 主机centos7-18 tcpdump抓包结果
  • tcpdump -nn -e -i enp0s5 host not 10.211.55.2 and icmp
    抓包排除ssh客户端 10.211.55.2
    -nn 两个 n 表示不解析域名和端口
    -e 在输出行打印出数据链路层的头部信息
    -i 抓指定接口(网卡)的数据包

[root@centos7-18 ~]# tcpdump -nn -e -i enp0s5 host not 10.211.55.2 and icmp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on enp0s5, link-type EN10MB (Ethernet), capture size 262144 bytes
// 00:1c:42:ae:b6:41（centos7-10 enp0s5）> 00:1c:42:60:87:b2（centos7-18 enp0s5）
19:59:52.186950 00:1c:42:ae:b6:41 > 00:1c:42:60:87:b2, ethertype IPv4 (0x0800), length 98: 10.211.55.10 > 172.16.1.200: ICMP echo request, id 2040, seq 1, length 64
// 00:1c:42:60:87:b2（centos7-18 enp0s5）> 00:1c:42:44:79:a5（centos7-22 enp0s5）
19:59:52.187068 00:1c:42:60:87:b2 > 00:1c:42:44:79:a5, ethertype IPv4 (0x0800), length 98: 10.211.55.10 > 172.16.1.200: ICMP echo request, id 2040, seq 1, length 64
// 00:1c:42:44:79:a5（centos7-22 enp0s5）> 00:1c:42:ae:b6:41（centos7-10 enp0s5）
19:59:52.187364 00:1c:42:44:79:a5 > 00:1c:42:ae:b6:41, ethertype IPv4 (0x0800), length 98: 172.16.1.200 > 10.211.55.10: ICMP echo reply, id 2040, seq 1, length 64
^C
3 packets captured
3 packets received by filter
0 packets dropped by kernel

总结

Linux 通过IP Forward 功能进行路由转发，根据已有路由配置信息把包送到合适的网络接口。