cloud-hypervisor can emulate one or more virtual network interfaces, represented at the hypervisor host by [tap devices](https://www.kernel.org/doc/Documentation/networking/tuntap.txt). This guide briefly describes, in a manual and distribution neutral way, how to setup and use networking with cloud-hypevisor.
Use one `--net` command-line argument from cloud-hypervisor to specify the emulation of one or more virtual NIC's. The example below instructs cloud-hypervisor to emulate for instance 2 virtual NIC's:
Different networking models can be used to provide external connectivity. In this example we will
use 2 linux bridges emulating 2 different networks. The integration bridge (ich-int) in this example will also be used
for external connectivity.
Create the bridges and connect the cloud-hypervisor tap devices to the bridges:
```bash
root@host:~# brctl addbr ich-int
root@host:~# brctl addbr ich-dpl
root@host:~# ip link set up ich-int
root@host:~# ip link set up ich-dpl
root@host:~# brctl addif ich-int ich0
root@host:~# brctl addif ich-dpl ich1
root@host:~# brctl show
bridge name bridge id STP enabled interfaces
ich-dpl 8000.067afc1b9a67 no ich1
ich-int 8000.725412ffce6f no ich0
```
This completes the layer 2 wiring: The cloud-hypervisor is now connected to the hypervisor host via the 2 linux bridges.
## IP (Layer 3) provisioning
### Hypervisor host
On the hypervisor host add the network gateway IP address of each network to the 2 linux bridges:
```bash
root@host:~# ip addr add 192.168.4.1/24 dev ich-int
root@host:~# ip addr add 10.0.1.1/24 dev ich-dpl
```
The routing table of the hypervisor host should now also have corresponding routing entries:
```bash
root@host:~# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.178.1 0.0.0.0 UG 600 0 0 wlan1
10.0.1.0 0.0.0.0 255.255.255.0 U 0 0 0 ich-dpl
192.168.4.0 0.0.0.0 255.255.255.0 U 0 0 0 ich-int
192.168.178.0 0.0.0.0 255.255.255.0 U 600 0 0 wlan1
```
### Virtual Machine
Within the virtual machine set the vNIC's to up state and provision the corresponding IP addresses on the 2 vNIC's. The steps outlined below use the ip command as an example. Alternative distribution specific procedures can also apply.
```bash
root@guest:~# ip link set up enp0s2
root@guest:~# ip link set up enp0s3
root@guest:~# ip addr add 192.168.4.2/24 dev enp0s2
root@guest:~# ip addr add 10.0.1.2/24 dev enp0s3
```
IP connectivity between the virtual machine and the hypervisor-host can be verified by sending
ICMP requests to the hypervisor-host for the gateway IP address from within the virtual machine:
```bash
root@guest:~# ping 192.168.4.1
PING 192.168.4.1 (192.168.4.1) 56(84) bytes of data.
64 bytes from 192.168.4.1: icmp_seq=1 ttl=64 time=0.456 ms
64 bytes from 192.168.4.1: icmp_seq=2 ttl=64 time=0.226 ms
root@guest:~# ping 10.0.1.1
PING 10.0.1.1 (10.0.1.1) 56(84) bytes of data.
64 bytes from 10.0.1.1: icmp_seq=1 ttl=64 time=0.449 ms
64 bytes from 10.0.1.1: icmp_seq=2 ttl=64 time=0.393 ms
```
The connection can now be used for instance to log into the virtual machine with
ssh under the precondition that the machine has an ssh daemon provisioned:
```bash
root@host:~# ssh root@192.168.4.2
The authenticity of host '192.168.4.2 (192.168.4.2)' can't be established.
ECDSA key fingerprint is SHA256:qNAUmTtDMW9pNuZARkpLQhfw+Yc1tqUDBrQp7aZGSjw.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.4.2' (ECDSA) to the list of known hosts.
root@192.168.4.2's password:
Linux cloud-hypervisor 5.2.0 #2 SMP Thu Jul 11 08:08:16 CEST 2019 x86_64
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Fri Jul 12 13:27:56 2019 from 192.168.4.1
root@guest:~#
```
## Internet connectivity
To enable internet connectivity a default gw and a nameserver has to be set within
the virtual machine:
```bash
root@guest:~# ip route add default via 192.168.4.1
root@guest:~# cat /etc/resolv.conf
options timeout:2
domain vallis.nl
search vallis.nl
nameserver 192.168.178.1
```
make sure that the default gateway of the hypervisor host (in this example host 192.168.178.1 which is an adsl router) has an entry in the routing table for the 192.168.4.0/24 network otherwise IP connectivity will not work.
```bash
root@guest:~# nslookup ftp.nl.debian.org
Server: 192.168.178.1
Address: 192.168.178.1#53
Non-authoritative answer:
cdn-fastly.deb.debian.org canonical name = prod.debian.map.fastly.net.
