What's eth0 used for in docker host machine - networking

Question

I'm using Docker on Windows. When I ssh to a docker host machine(local VM) and type ifconfig, normally we get something like this:
docker#master:~$ ifconfig
docker0 Link encap:Ethernet HWaddr 02:42:82:A3:2D:FB
inet addr:172.17.0.1 Bcast:0.0.0.0 Mask:255.255.0.0
UP BROADCAST MULTICAST MTU:1500 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)
eth0 Link encap:Ethernet HWaddr 08:00:27:E8:A3:F6
inet addr:10.0.2.15 Bcast:10.0.2.255 Mask:255.255.255.0
inet6 addr: fe80::a00:27ff:fee8:a3f6/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:243 errors:0 dropped:0 overruns:0 frame:0
TX packets:235 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:39044 (38.1 KiB) TX bytes:39544 (38.6 KiB)
eth1 Link encap:Ethernet HWaddr 08:00:27:83:CF:41
inet addr:192.168.99.101 Bcast:192.168.99.255 Mask:255.255.255.0
inet6 addr: fe80::a00:27ff:fe83:cf41/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:297 errors:0 dropped:0 overruns:0 frame:0
TX packets:227 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:29987 (29.2 KiB) TX bytes:32525 (31.7 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:32 errors:0 dropped:0 overruns:0 frame:0
TX packets:32 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1
RX bytes:2752 (2.6 KiB) TX bytes:2752 (2.6 KiB)
I know that docker0 is the bridge network created by Docker, eth1 is the interface connects to the outer world, lo is the loopback interface, my question is what's eth0 here used for?

Answer 1

I think I got the point. When I come to the VirtualBox Network Settings, I found there're 2 network cards, and the first one using NAT with port forwarding.
Name:ssh | Host Port:53289 | Guest Port:22
So I thought the eth0 is used for ssh connection by docker client. That's why there's no such an interface in a normal Linux OS(rather than this Boot2Docker local VM).
Different ideas are welcome!