实验：主机间跨网络通信
实验拓扑图：
第一步：创建四个虚拟机
第二步：配置vmnet6和vmnet8网段
vmnet6:10.0.0.0/8
vmnet8:192.168.38.0/24
vmnet0:172.18.0.0/24
三、如上图所示，配置好每个虚拟机的网卡类型
四、配置IP
第一个虚拟机
[root@localhost ~]# cat /etc/sysconfig/network-scripts/ifcfg-ens33
TYPE=Ethernet
BOOTPROTO=static
IPADDR=192.168.38.123
NETMASK=255.255.255.0
GATEWAY=192.168.38.2
NAME=ens33
DEVICE=ens33
ONBOOT=yes
[root@localhost ~]# systemctl restart network第二个虚拟机
[root@localhost ~]# cat /etc/sysconfig/network-scripts/ifcfg-ens33
TYPE=Ethernet
BOOTPROTO=static
IPADDR=192.168.38.200
NETMASK=255.255.255.0
GATEWAY=192.168.38.2
NAME=ens33
DEVICE=ens33
ONBOOT=yes
[root@localhost ~]# cat /etc/sysconfig/network-scripts/ifcfg-ens37
TYPE=Ethernet
BOOTPROTO=static
IPADDR=10.0.0.200
NETMASK=255.0.0.0
GATEWAY=10.0.0.1
NAME=ens37
DEVICE=ens37
ONBOOT=yes
[root@localhost ~]# systemctl restart network第三个虚拟机
[root@localhost ~]# cat /etc/sysconfig/network-scripts/ifcfg-ens33
TYPE=Ethernet
BOOTPROTO=static
IPADDR=10.0.0.201
NETMASK=255.0.0.0
GATEWAY=10.0.0.1
NAME=ens33
DEVICE=ens33
ONBOOT=yes
[root@localhost ~]# cat /etc/sysconfig/network-scripts/ifcfg-ens37
TYPE=Ethernet
BOOTPROTO=static
IPADDR=172.18.28.201
NETMASK=255.255.0.0
GATEWAY=172.18.0.1
NAME=ens37
DEVICE=ens37
ONBOOT=yes
[root@localhost ~]# systemctl restart network第四个虚拟机
[root@localhost ~]# cat /etc/sysconfig/network-scripts/ifcfg-ens33
TYPE=Ethernet
BOOTPROTO=static
IPADDR=172.18.28.202
NETMASK=255.255.0.0
GATEWAY=172.18.0.1
NAME=ens33
DEVICE=ens33
ONBOOT=yes
[root@localhost ~]# systemctl restart network五、配置路由规则
现在B还ping不通A
[root@b ~]# ping 192.168.38.123
PING 192.168.38.123 (192.168.38.123) 56(84) bytes of data.
From 172.18.28.28 icmp_seq=1 Redirect Network(New nexthop: 172.18.0.1)
From 172.18.28.28: icmp_seq=1 Redirect Network(New nexthop: 172.18.0.1)A的默认网关应该是192.168.38.200（或者给A加一条路由，让A知道172.18网段是要通过192.168.38.200出去的，不然数据包全发到192.168.38.2去了）
[root@localhost ~]# ip route add default via 192.168.38.200R1走172.18网段通过10.0.0.201
[root@localhost ~]# ip route add 172.18.0.0/16 via 10.0.0.201R2走192.168.38网段通过10.0.0.200
[root@r2 ~]# ip route add 192.168.38.0/24 via 10.0.0.200B的默认网关应该是172.18.28.201
[root@b ~]# ip route add default via 172.18.28.201六、第二三个虚拟机开启路由转发
第二个和第三个虚拟机都要执行
[root@localhost ~]# echo "net.ipv4.ip_forward = 1" >> /etc/sysctl.d/ip_forward.conf
[root@localhost ~]# sysctl -p /etc/sysctl.d/ip_forward.conf
net.ipv4.ip_forward = 1七、接下来就是见证奇迹的时刻
B ping A
[root@b ~]# ping 192.168.38.123 -c3
PING 192.168.38.123 (192.168.38.123) 56(84) bytes of data.
64 bytes from 192.168.38.123: icmp_seq=1 ttl=62 time=4.83 ms
64 bytes from 192.168.38.123: icmp_seq=2 ttl=62 time=1.03 ms
64 bytes from 192.168.38.123: icmp_seq=3 ttl=62 time=1.12 ms
--- 192.168.38.123 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 1.034/2.329/4.832/1.770 msA ping B (第一次实验做完后NAT就可以直接ping到桥接了，不知道什么原因)
[root@localhost ~]# ping 172.18.28.202 -c3
PING 172.18.28.202 (172.18.28.202) 56(84) bytes of data.
64 bytes from 172.18.28.202: icmp_seq=1 ttl=62 time=2.20 ms
64 bytes from 172.18.28.202: icmp_seq=2 ttl=62 time=1.14 ms
64 bytes from 172.18.28.202: icmp_seq=3 ttl=62 time=0.876 ms
--- 172.18.28.202 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 0.876/1.408/2.202/0.573 msA到B怎么走的：
[root@localhost ~]# tracepath -n 172.18.28.202
1?: [LOCALHOST] pmtu 1500
1: 192.168.38.200 0.558ms
1: 192.168.38.200 1.848ms
2: 10.0.0.201 2.290ms
3: 172.18.28.202 4.786ms reached
Resume: pmtu 1500 hops 3 back 3 B到A怎么走的
[root@b ~]# tracepath -n 192.168.38.123
1?: [LOCALHOST] pmtu 1500
1: 172.18.28.201 0.887ms
1: 172.18.28.201 0.863ms
2: 10.0.0.200 5.798ms
3: 192.168.38.123 9.648ms reached
Resume: pmtu 1500 hops 3 back 3 现在虚拟机不知道怎么了默认NAT就能ping到桥接的虚拟机，现在tracepath看一下(这是新的一台虚拟机)
# 能ping通
[qqq@ubuntu ~]$ ping 172.18.28.202 -c2
PING 172.18.28.202 (172.18.28.202) 56(84) bytes of data.
64 bytes from 172.18.28.202: icmp_seq=1 ttl=128 time=2.15 ms
64 bytes from 172.18.28.202: icmp_seq=2 ttl=128 time=0.738 ms
--- 172.18.28.202 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 3ms
rtt min/avg/max/mdev = 0.738/1.442/2.146/0.704 ms
#看一下怎么走的
[qqq@ubuntu ~]$ tracepath -n 172.18.28.202
1?: [LOCALHOST] pmtu 1500
1: 192.168.38.2 0.480ms
1: 192.168.38.2 0.120ms
2: no reply
3: no reply
4: no reply
... (确实是到了NAT桥那里，后面一直noreply了)持久化路由表
思路:可以把添加路由的命令写入开机启动文件
方法一：
写入rc.local文件
方法二（推荐）：
# CentOS7可行，其他未测
[root@localhost ~]# ip route > /etc/sysconfig/network-scripts/route-ens33