我通过 Oracle VirtualBox 设置了 3 个虚拟机：Ubuntu、Fedora 和 CentOS。Ubuntu 机器的设置如下：
kuyu@ub16:~$ ifconfig
enp0s3 Link encap:Ethernet HWaddr 08:00:27:ed:19:9f
inet addr:172.25.1.4 Bcast:172.25.1.255 Mask:255.255.255.0
inet6 addr: fe80::7d42:e5b6:7818:df37/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:23245 errors:0 dropped:0 overruns:0 frame:0
TX packets:18488 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:21373422 (21.3 MB) TX bytes:3230755 (3.2 MB)
enp0s8 Link encap:Ethernet HWaddr 08:00:27:a4:79:fe
inet6 addr: fe80::5d4e:ef97:3c34:f2b6/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1582 errors:0 dropped:0 overruns:0 frame:0
TX packets:70 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:119897 (119.8 KB) TX bytes:9194 (9.1 KB)
enp0s9 Link encap:Ethernet HWaddr 08:00:27:3a:28:14
inet6 addr: fe80::118f:71e1:f2b2:f582/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1586 errors:0 dropped:0 overruns:0 frame:0
TX packets:69 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:120766 (120.7 KB) TX bytes:8852 (8.8 KB)
enp0s10 Link encap:Ethernet HWaddr 08:00:27:3a:23:39
inet addr:10.0.3.4 Bcast:10.0.3.255 Mask:255.255.255.0
inet6 addr: fe80::1013:fee6:cdd6:4ba4/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:16377 errors:0 dropped:0 overruns:0 frame:0
TX packets:12869 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:15323241 (15.3 MB) TX bytes:2256638 (2.2 MB)
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:2304 errors:0 dropped:0 overruns:0 frame:0
TX packets:2304 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1
RX bytes:292108 (292.1 KB) TX bytes:292108 (292.1 KB)
kuyu@ub16:~$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default 10.0.3.1 0.0.0.0 UG 100 0 0 enp0s10
default 172.25.1.1 0.0.0.0 UG 101 0 0 enp0s3
10.0.3.0 * 255.255.255.0 U 100 0 0 enp0s10
link-local * 255.255.0.0 U 1000 0 0 enp0s10
172.25.1.0 * 255.255.255.0 U 100 0 0 enp0s3
Fedora 机器设置如下：
[kuyu@localhost ~]$ ifconfig
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.0.2.15 netmask 255.255.255.0 broadcast 10.0.2.255
inet6 fe80::a06b:59f9:ecd2:5f4f prefixlen 64 scopeid 0x20<link>
ether 08:00:27:cc:b4:fe txqueuelen 1000 (Ethernet)
RX packets 15606 bytes 10210208 (9.7 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 10377 bytes 1378129 (1.3 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
enp0s8: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.0.3.5 netmask 255.255.255.0 broadcast 10.0.3.255
inet6 fe80::5081:a65:f591:5587 prefixlen 64 scopeid 0x20<link>
ether 08:00:27:10:4b:c6 txqueuelen 1000 (Ethernet)
RX packets 185 bytes 27128 (26.4 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 314 bytes 44983 (43.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
enp0s9: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.2.5 netmask 255.255.255.0 broadcast 192.168.2.255
inet6 fe80::ea6c:3aa1:5fc9:bdff prefixlen 64 scopeid 0x20<link>
ether 08:00:27:e1:62:f4 txqueuelen 1000 (Ethernet)
RX packets 62 bytes 12502 (12.2 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 234 bytes 34491 (33.6 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 1000 (Local Loopback)
RX packets 36 bytes 3112 (3.0 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 36 bytes 3112 (3.0 KiB)
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 00:00:00:00:00:00 txqueuelen 1000 (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
[kuyu@localhost ~]$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default gateway 0.0.0.0 UG 100 0 0 enp0s3
default gateway 0.0.0.0 UG 101 0 0 enp0s9
default gateway 0.0.0.0 UG 102 0 0 enp0s8
10.0.2.0 0.0.0.0 255.255.255.0 U 100 0 0 enp0s3
10.0.3.0 0.0.0.0 255.255.255.0 U 100 0 0 enp0s8
192.168.2.0 0.0.0.0 255.255.255.0 U 100 0 0 enp0s9
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0
CentOS 机器设置如下：
[kuyu@localhost ~]$ ifconfig
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.25.1.5 netmask 255.255.255.0 broadcast 172.25.1.255
inet6 fe80::1f36:5e13:45ae:b7d1 prefixlen 64 scopeid 0x20<link>
ether 08:00:27:f4:fd:91 txqueuelen 1000 (Ethernet)
RX packets 15070 bytes 21673274 (20.6 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 7401 bytes 471787 (460.7 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
enp0s8: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet6 fe80::bd87:67c1:8b39:f511 prefixlen 64 scopeid 0x20<link>
ether 08:00:27:30:f3:fa txqueuelen 1000 (Ethernet)
RX packets 1442 bytes 107149 (104.6 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 56 bytes 6524 (6.3 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
enp0s9: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet6 fe80::e6a5:62c4:3dfa:b841 prefixlen 64 scopeid 0x20<link>
ether 08:00:27:b9:cf:71 txqueuelen 1000 (Ethernet)
RX packets 1403 bytes 102963 (100.5 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 17 bytes 2954 (2.8 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
enp0s10: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.2.4 netmask 255.255.255.0 broadcast 192.168.2.255
inet6 fe80::3c3e:1a03:e554:514d prefixlen 64 scopeid 0x20<link>
ether 08:00:27:bd:1f:4a txqueuelen 1000 (Ethernet)
RX packets 131 bytes 23156 (22.6 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 339 bytes 57279 (55.9 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 134 bytes 11636 (11.3 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 134 bytes 11636 (11.3 KiB)
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:bb:2b:56 txqueuelen 1000 (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
[kuyu@localhost ~]$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default gateway 0.0.0.0 UG 100 0 0 enp0s3
default gateway 0.0.0.0 UG 101 0 0 enp0s10
172.25.1.0 0.0.0.0 255.255.255.0 U 100 0 0 enp0s3
192.168.2.0 0.0.0.0 255.255.255.0 U 100 0 0 enp0s10
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0
Fedora 机器中启用了路由：
[kuyu@localhost ~]$ sudo sysctl -p /etc/sysctl.conf
net.ipv4.ip_forward = 1
Ubuntu 机器能够 ping Fedora 机器：
kuyu@ub16:~$ ping 10.0.3.5
PING 10.0.3.5 (10.0.3.5) 56(84) bytes of data.
64 bytes from 10.0.3.5: icmp_seq=1 ttl=64 time=2.39 ms
64 bytes from 10.0.3.5: icmp_seq=2 ttl=64 time=1.53 ms
同样，CentOS 机器可以 ping Fedora 机器：
[kuyu@localhost ~]$ ping 192.168.2.5
PING 192.168.2.5 (192.168.2.5) 56(84) bytes of data.
64 bytes from 192.168.2.5: icmp_seq=1 ttl=64 time=1.63 ms
64 bytes from 192.168.2.5: icmp_seq=2 ttl=64 time=1.14 ms
64 bytes from 192.168.2.5: icmp_seq=3 ttl=64 time=1.42 ms
但是，Ubuntu 计算机无法通过 Fedora 计算机 ping 通 CentOS 计算机：
kuyu@ub16:~$ ping 192.168.2.4
PING 192.168.2.4 (192.168.2.4) 56(84) bytes of data.
^C
--- 192.168.2.4 ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 4050ms
同样，CentOS 机器无法通过 Fedora 机器 ping 通 Ubuntu 机器：
[kuyu@localhost ~]$ ping 10.0.3.4
PING 10.0.3.4 (10.0.3.4) 56(84) bytes of data.
^C
--- 10.0.3.4 ping statistics ---
4 packets transmitted, 0 received, 100% packet loss, time 3004ms
我的问题是如何修复机器配置，以便 Ubuntu 机器可以通过 Fedora 机器 ping 通 CentOS 机器（反之亦然）？
答案1
您的 Fedora 机器可能/很可能具有默认防火墙，阻止了数据包的转发。
尝试运行
/sbin/iptables -I 转发 -j 接受
允许通过该箱转发。
如果这不起作用，我会打破 tcpdump（然后在盒子之间启动 ping 并查看它卡在哪里）