Virt-manager network setup
We assume that virt-manager has been installed
in a Linux host, and
at least one guest Linux system has been installed
and is running.
The first thing to learn with virt-manager is how to find the settings.
Under View on the QEMU/KVM Window, there are two options
- Console which means show the running guest console
- Details which means show the settings
You can toggle between them.
You can change the settings for a guest VM at any time, they are not fixed when it is installed. It is best to change settings with the guest not running. If you change settings with the guest running, they do not apply until the next boot.
Default network settings
The guest VM is by default connected to the host system by a network bridge. If we look at the host network devices with the ip command we see
$ ip addr
.....
5: virbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 52:54:00:78:7c:5d brd ff:ff:ff:ff:ff:ff
inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
valid_lft forever preferred_lft forever
That device virbr0 is a virtual bridge between the host and guest systems. The guests under virt-manager ( there can be more than one) are on a virtual network with address 192.168.122.0. The bridge is address 192.168.122.1 on that network (as seen by the host). The host can route packets to that network via the bridge interface, in exactly the same way as it routes packets to an ethernet port or other interfaces.
To find the IP address of a guest on the above virtual network, one has to use the ip command in the guest.
$ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 52:54:00:59:a0:69 brd ff:ff:ff:ff:ff:ff
inet 192.168.122.45/24 brd 192.168.122.255 scope global dynamic noprefixroute eth0
valid_lft 2932sec preferred_lft 2932sec
inet6 fe80::994e:fcd3:91f3:6f30/64 scope link noprefixroute
valid_lft forever preferred_lft forever
We see 2 interfaces, lo which is the guest itself, and eth0 which is the guest’s interface to the virtual network. We can see now that our guest has IP address 192.168.122.45 on the virtual network.
We had to go into the guest to find its IP address, because virt-manager by default uses NAT (Network Address Translation) which means that one can not obtain the IP address of the guest from anywhere outside the guest.
One can operate virt-manager with just a bridge and no NAT. To do that got to View → Details → Add Hardware → Network and change the Network Source setting from Virtualnetwork default:NAT to Bridge Device. Without NAT, one can scan the virtual network from the host with a tool like nmap and find the guest IP addresses. That is about the only difference. We recommend using virt-manager with the default NAT setting.
From the host one can ping the guest using its IP number,
and one can ping the bridge using IP=192.168.122.1.
From the guest one can ping the host using either the hostname,
or the IP number of any of the hosts interfaces,
and one can ping the bridge using IP=192.168.122.1.
The guest does not know the host’s hostname, the name is
unresolved in the guest, but the ping packet is routed to the host where
it gets resolved.
Using hostnames
While one can communicate with a guest in virt-manager
using its IP address, it is more convenient to use hostnames. To do that we just need to set up hostnames in the file /etc/hosts
To achieve that , we need to add an entry to the file
/etc/hosts in the host system
$ cat /etc/hosts
# IP-number Domain-name Hostname
......
192.168.32.6 trinity.colrose.com.au trinity
192.168.32.7 mary.colrose.com.au mary
192.168.122.45 mxvm.colrose.com.au mxvm
The entry mxvm is the hostname of the guest system.
The host system’s hostname is trinity and mary is another
computer on the local network.
With this setup one can do, from the host
$ ping mxvm
PING mxvm.colrose.com.au (192.168.122.45) 56(84) bytes of data.
64 bytes from mxvm.colrose.com.au (192.168.122.45): icmp_seq=1 ttl=64 time=0.199 ms
From the guest, one can always ping the host
$ ping trinity
PING trinity.colrose.com.au (192.168.32.6) 56(84) bytes of data.
64 bytes from trinity.colrose.com.au (192.168.32.6): icmp_seq=1 ttl=64 time=0.246 ms
because the guest will route the unresolved ping packed to the host
as explained above.
From the guest, one can also ping any other computer or
device on the local net ( such as mary), and any
internet site that the host can access.
We use ping here just to show that communication is established.
If ping is successful, we can proceed with data sharing.
Recommendation
When you setup virt-manager, get familiar with its virtual network.
Everything you do to share data between host and guest, or between multiple guests, depends on understanding the virtual network.
Links
https://gulraezgulshan.medium.com/virtual-networking-in-linux-b1abcb983e72