环境说明： 同一交互机物理隔断的2个私有网络,每个网络中分别为CentOS 6 * 1, CentOS 7 * 1
好的，现在我们开始~
1.首先我们先看一下2台主机的网络配置信息 先看CentOS 6的：
代码语言：javascript复制[root@Centos6 ~]# ifconfig
eth1 Link encap:Ethernet HWaddr 00:0C:29:40:43:BC
inet addr:192.168.10.10 Bcast:192.168.10.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe40:43bc/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:84 errors:0 dropped:0 overruns:0 frame:0
TX packets:56 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:14932 (14.5 KiB) TX bytes:9438 (9.2 KiB)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
[root@Centos6 ~]# ping 192.168.20.20
connect: Network is unreachable
[root@Centos6 ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface然后是CentOS 7的：
代码语言：javascript复制[root@Centos7 ~]# ifconfig
ens33: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.20.20 netmask 255.255.255.0 broadcast 192.168.20.255
inet6 fe80::20c:29ff:fe03:b85f prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:03:b8:5f txqueuelen 1000 (Ethernet)
RX packets 61 bytes 6951 (6.7 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 100 bytes 15953 (15.5 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 1 (Local Loopback)
RX packets 268 bytes 21616 (21.1 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 268 bytes 21616 (21.1 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
[root@Centos7 ~]# ping 192.168.10.10
connect: Network is unreachable
[root@Centos7 ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.20.0 0.0.0.0 255.255.255.0 U 0 0 0 ens332.那么，如果要让这2台不同网段的主机能够通信该怎么办呢？
嗯，当然有办法，而且有3种：
- 新增一台拥有2张网卡的服务器(或在交换机上进行相关设置)，分别指向192.168.10.0/24和192.168.20.0/24的网络;
- 为环境中的Centos 6或7中任意一台服务器添加一张网卡，指向对方网络，然后开启内核转发功能;
- 使用默认路由;
这里我们以方法三为例 另2种方法参见本博其他文章 此处不赘述
3.由于10.0和20.0这2个私有网络是交换机物理隔断的，所以我们可以通过添加默认网关的方法实现通信(当然还有第二步中提到的其他方法)，但不同的是指向的网关为自己同交换机的直连网口地址
代码语言：javascript复制[root@Centos6 ~]# route add default gw 192.168.10.10 #Centos 6上
[root@Centos6 ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.10.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
0.0.0.0 192.168.10.10 0.0.0.0 UG 0 0 0 eth1
[root@Centos7 ~]# route add default gw 192.168.20.20 #Centos 7上
[root@Centos7 ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.20.20 0.0.0.0 UG 0 0 0 ens33
192.168.20.0 0.0.0.0 255.255.255.0 U 0 0 0 ens334.接下来，我们进行PING测试并在Centos 7上抓包
代码语言：javascript复制[root@Centos6 ~]# ping 192.168.20.20 #Centos 6上
PING 192.168.20.20 (192.168.20.20) 56(84) bytes of data.
64 bytes from 192.168.20.20: icmp_seq=1 ttl=64 time=0.646 ms
64 bytes from 192.168.20.20: icmp_seq=2 ttl=64 time=0.251 ms
64 bytes from 192.168.20.20: icmp_seq=3 ttl=64 time=1.37 ms
64 bytes from 192.168.20.20: icmp_seq=4 ttl=64 time=1.19 ms
64 bytes from 192.168.20.20: icmp_seq=5 ttl=64 time=0.269 ms
64 bytes from 192.168.20.20: icmp_seq=6 ttl=64 time=2.11 ms
64 bytes from 192.168.20.20: icmp_seq=7 ttl=64 time=0.652 ms
[root@Centos7 ~]# tcpdump -i ens33 -nn icmp #Centos 7上
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on ens33, link-type EN10MB (Ethernet), capture size 65535 bytes
05:16:44.057527 IP 192.168.10.10 > 192.168.20.20: ICMP echo request, id 33029
, seq 149, length 64
05:16:44.057580 IP 192.168.20.20 > 192.168.10.10: ICMP echo reply, id 33029,
seq 149, length 64
05:16:45.058726 IP 192.168.10.10 > 192.168.20.20: ICMP echo request, id 33029
, seq 150, length 64
05:16:45.058806 IP 192.168.20.20 > 192.168.10.10: ICMP echo reply, id 33029,
seq 150, length 64
05:16:46.059739 IP 192.168.10.10 > 192.168.20.20: ICMP echo request, id 33029
, seq 151, length 64
05:16:46.059886 IP 192.168.20.20 > 192.168.10.10: ICMP echo reply, id 33029,
seq 151, length 64
05:16:47.060638 IP 192.168.10.10 > 192.168.20.20: ICMP echo request, id 33029
, seq 152, length 645.至此，环境中的两个不同网段的主机已成功互通。
