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I just took over a very old network cluster(no documents and manual left) so I have to imagine the meaning of configuration by myself. Some of the servers' IP configure as following(when I issue ifconfig)

bond0: flags=5187<UP,BROADCAST,RUNNING,MASTER,MULTICAST>
 inet 10.1.237.11 netmask 255.255.255.192 broadcast 10.1.237.63
 ether 6c:90:af:68:5a:28 txqueuelen 0 (Ethernet)

bond0.901: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>
 inet 147.146.67.13 netmask 255.255.255.240 broadcast 147.146.67.15
 ether 6c:90:af:68:5a:28 txqueuelen 0 (Ethernet)

bond0.901:1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>
 inet 147.185.211.5 netmask 255.255.255.0 broadcast 147.185.211.255
 ether 6c:90:af:68:5a:28 txqueuelen 0 (Ethernet)

eth2: flags=6211<UP,BROADCAST,RUNNING,SLAVE,MULTICAST>
 ether 6c:90:af:68:5a:28 txqueuelen 1000 (Ethernet)

eth3: flags=6211<UP,BROADCAST,RUNNING,SLAVE,MULTICAST>
 ether 6c:90:af:68:5a:28 txqueuelen 1000 (Ethernet)

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
 inet 127.0.0.1 netmask 255.0.0.0
 loop txqueuelen 0 (Local Loopback)

From the same mac address, I can see there is only one NIC. I was told that bond0 for inner IP, bond0.901 for internet IP, bond0.901:1 for Anycast IP. So my question is that what do eth2 and eth3 for and why one of the virtual NIC called bond0, is there anything need to be bond together?

When I issued the command: lspci|grep Ether, I got the following:

01:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
01:00.1 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
01:00.2 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
01:00.3 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
04:00.0 Ethernet controller: Intel Corporation 82599ES 10-Gigabit SFI/SFP+ Network Connection (rev 01)
04:00.1 Ethernet controller: Intel Corporation 82599ES 10-Gigabit SFI/SFP+ Network Connection (rev 01)
07:00.0 Ethernet controller: Intel Corporation 82599ES 10-Gigabit SFI/SFP+ Network Connection (rev 01)
07:00.1 Ethernet controller: Intel Corporation 82599ES 10-Gigabit SFI/SFP+ Network Connection (rev 01)
09:00.0 Ethernet controller: Intel Corporation 82599ES 10-Gigabit SFI/SFP+ Network Connection (rev 01)
09:00.1 Ethernet controller: Intel Corporation 82599ES 10-Gigabit SFI/SFP+ Network Connection (rev 01)

Does the above mean I have 10 physical Network cards please?

I suspect that eth2, and eth3 are the physical devices that make up the bond0 device. See the master/slave flags. But your system probably has 2 physical interfaces, these are being combined in some kind of fault tolerance, or link aggregation setup. Try looking at the output of these tools which query the physical hardware lspci | grep Ether, or lshw -class network. You probably will see at least 2 interfaces.

bond0: flags=5187<UP,BROADCAST,RUNNING,MASTER,MULTICAST>
eth2: flags=6211<UP,BROADCAST,RUNNING,SLAVE,MULTICAST>
eth3: flags=6211<UP,BROADCAST,RUNNING,SLAVE,MULTICAST>

The contents of the file /proc/net/bonding/bond0 would tell you more.

• Bonding docs https://wiki.linuxfoundation.org/networking/bonding#ethernet-device-renaming
  

The bond0.901 is a virtual device allowing for a tagged vlan 901 on bond0.

The bond0.901:1 is just an secondary IP address for the bond0.901 VLAN 901 interface. This is not a real interface, or even a virtual one. This 'interface' is just just a way for ifconfig to show you the second address. But it is a deprecated tool that can give you confusing output like this. Use ip addr, or ip link instead.