How to Resolve VirtualBox Host-Only IP by VM Name

centoshost-onlynetworkingvirtualbox

I have a Win 10 physical host with VirtualBox v6.1.34 and a guest OS of CentOS 7.

As a default setting, the VirtualBox Host-Only Ethernet Adapter is on 192.168.56.1/24, and the guest connects to this network adapter in Automatic mode.

After booting up, the guest acquired the address through DHCP, and I verified it by calling the command ifconfig on the guest. To be simple, the hostname of the guest OS is the same as the VM's name.

I also followed this link and verified the record of the DHCP lease. By the way, the leasing record contains the IP and MAC addresses, but I didn't find any indication about either hostname, domain name, or VirtualBox VM name.

However, I could not ping the guest by the VM's name on the physical host. As said before, it is the same as the hostname.

I tried ping hostname and ping hostname.local but they didn't work.
With the known address, ping 192.168.56.xxx works.

Please let me know if you need more information.

I am new to networking, so I would highly appreciate your suggestions with some pointers on the basic concepts, e.g. subnet, gateway, router, DNS, DHCP, etc.

Best Answer

Name lookup based on DHCP leases is done via local DNS that needs to be provided by the DHCP server in question (i.e. by VirtualBox's internal "host-only" DHCP service). Synchronization of DHCP leases to DNS entries isn't inherently built-in to DHCP but is a feature that needs to be separately implemented by the software's authors, and as far as I can see in VirtualBox's Dhcpd source code, such integration isn't implemented at all.

(In addition, the client (i.e. your host OS) also needs to be configured to actually use that DNS server. This is also unlikely to be the case, as VirtualBox's DNS is meant for VMs so it forwards the requests to wherever the host OS configuration tells it to... so if the host tries to use VirtualBox's DNS, you're going to get a DNS request loop and won't be able to resolve anything at all.)

Direct (non-DNS) name lookup is usually based on the mDNS or LLMNR protocols. For bare host or host.local names to work, the VM needs to actually serve at least one of those protocols – usually via avahi-daemon for mDNS, via systemd-networkd for LLMNR (or both). Install one of those services and make sure the VM's firewall allows the inbound UDP query packets.

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OK, so there are 2 ways of sort of doing this.

1) Use the VirtualBox NAT network on the client. This doesn't provide a direct route from your host machine, but you can set preferences to forward ports. Kind of a pain to set up, but if the host machine was Windows or a Mac this is what I'd probably do, mostly because I'm not sure on firewalling/natting/routing capabilities on those systems (pretty sure Mac wouldn't have an issue, but Windows is unknown to me)

2) Use the VirtualBox Host Only Network. From your description, this may be better. Be aware that you will need to change the firewall script to point to whatever device is connected.... Here's teh details.

On the host machine, first set up the Host Only Network in your vbox preferences. In the Manager, click File and then Preferences, and then select Network. Flip over to Host Only, and then add one if needed. Here's what mine looks like:

Next, on the host, configure the vboxnet0 interface. It automagically just happens for me, setting my host machine to the .1 address in the subnet. Here's output of ifconfig on my host, referencing my ethernet and vboxnet0 address.

In your guest machine, set the network to some address in your subnet (even with the DHCP server enabled, this makes it easier to get gateway/dns server) and set a nameserver in the usual way (ie, edit /etc/network/interfaces and set the static address/netmask/gateway there, then edit /etc/resolv.conf and set a name server there).

At this point, your host machine and your guest machine should be able to communicate back and forth with no issues. You may want to put appropriate entries in /etc/hosts so you don't have to enter the IPs everywhere...

The last step is to get internet going for the guest. This is a simple matter of turning the host into a router. Since the vboxnet0 interface doesn't come up until vbox is up and running, you don't want to do this at boot time for the host.

A simple firewall script to allow the guest vm to access the world, and the host machine can still access the world and the guest in the vboxonly network. Be aware that this script could be MUCH more secure. As it is, it would accept some client on whatever network the host is connected to using your host machine as a gateway to the guest vm.

#!/bin/bash

echo 1 > /proc/sys/net/ipv4/ip_forward

iptables=`which iptables`

$iptables -F

/sbin/iptables -t nat -A POSTROUTING -o enp2s0 -j MASQUERADE

$iptables -A FORWARD -i enp2s0 -o vboxnet0 -j ACCEPT
$iptables -A FORWARD -i vboxnet0 -o enp2s0 -j ACCEPT

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