I've been working with a question on SO, and noticed something about my own setup that struck me as odd. Here's the background.
I've built scores of VBox VMs on my office workstations at my last two employers (retired about this time last year). To keep them completely off the company network, I set them up with a HOSTONLY adapter. The installation of VBox itself would set up a network adapter on the Windows host machine. An ipconfig would reveal that adapter identified as "Ethernet adapter VirtualBox Host-Only Network". It would, by default, have an ip address of 192.168.56.1. When creating VMs with a HOSTONLY adapter, I'd manually assign the vm's with an IP in the same subnet of 192.168.56, typically starting with 100 for the last octet. All was well with the world and made perfect sense.
Since retiring, I've maintained a couple of VM's on one of my personal laptops which runs Ubuntu. The vm's run either Oracle Linux or Windows. But my every day laptop is a different machine, so I configured the VMs on the ubuntu laptop to use a bridged adapter. For their manually assigned IP, I give them an address in the same subnet as the one the host is running on. In this case, an ifconfig of the host, Ubuntu, machine shows:
ed@ed-Gazelle-00:~$ ifconfig
enp2s0f1: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether 80:fa:5b:35:68:a7 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
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 9004 bytes 710343 (710.3 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 9004 bytes 710343 (710.3 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
wlp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.68.55 netmask 255.255.252.0 broadcast 192.168.71.255
inet6 fe80::2415:11f2:bf66:6d prefixlen 64 scopeid 0x20<link>
ether e4:a4:71:f2:0c:56 txqueuelen 1000 (Ethernet)
RX packets 1902448 bytes 512096613 (512.0 MB)
RX errors 0 dropped 178 overruns 0 frame 0
TX packets 1395958 bytes 1156196724 (1.1 GB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
ed@ed-Gazelle-00:~$
Note adapter wlp3s0, with an ip of 192.168.68.55. So I give my vm's a manual ip address in the 192.168.68 subnet.
But notice adapter enp2s0f1, has no IP address. Since I was setting this up for bridged, I never actually looked for the VBox adapter. And the vbox network config shows it running 'vboxnet0' on ip 192.168.56.1 - just as I'd expect. (Sorry, can't seem to get a screen shot from that machine).
So I'm wondering two things. 1) what is that adapter, reported by ifconfig on the ubuntu host, that does not have an IP, and 2) where is the vbox hostonly adpter that should be running on the host?
I fully expect the answer to result in a face-palm, and a Homer Simpson "DOH!".