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How to use networking
cloud-hypervisor can emulate one or more virtual network interfaces, represented at the hypervisor host by tap devices. This guide briefly describes, in a manual and distribution neutral way, how to setup and use networking with cloud-hypevisor.
Start cloud-hypervisor with net devices
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:
./cloud-hypervisor \
--cpus 4 \
--memory "size=512M" \
--disk my-root-disk.img \
--kernel my-vmlinux.bin \
--cmdline "console=ttyS0 reboot=k panic=1 nomodules root=/dev/vda3" \
--net tap=ich0,mac=a4:a1:c2:00:00:01,ip=192.168.4.2,mask=255.255.255.0 \
tap=ich1,mac=a4:a1:c2:00:00:02,ip=10.0.1.2,mask=255.255.255.0
The --net argument takes 1 or more space-separated strings of key value pairs containing the following 4 keys or fields:
| Name | Purpose | Optional |
|---|---|---|
| tap | tap device name | Yes |
| mac | vNIC mac address | Yes |
| ip | tap IP IP address | yes |
| mask | tap IP netmask | Yes |
Configure the tap devices
After starting cloud-hypervisor as shown above, 2 tap devices with state down will become available at the host:
root@host:~# ip link show ich0
78: ich0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 72:54:12:ff:ce:6f brd ff:ff:ff:ff:ff:ff
root@host:~# ip link show ich1
79: ich1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 06:7a:fc:1b:9a:67 brd ff:ff:ff:ff:ff:ff
Set the tap devices to up state:
root@host:~# ip link set up ich0
root@host:~# ip link set up ich1
root@host:~# ip link show ich0
78: ich0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN mode DEFAULT group default qlen 1000
link/ether 72:54:12:ff:ce:6f brd ff:ff:ff:ff:ff:ff
root@host:~# ip link show ich1
79: ich1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN mode DEFAULT group default qlen 1000
link/ether 06:7a:fc:1b:9a:67 brd ff:ff:ff:ff:ff:ff
Connect tap devices
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:
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:
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:
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.
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:
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:
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:
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.
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.
Name: prod.debian.map.fastly.net
Address: 151.101.36.204
root@guest:~# apt-get update
Ign:1 http://cdn-fastly.deb.debian.org/debian stretch InRelease
Get:2 http://cdn-fastly.deb.debian.org/debian stretch Release [118 kB]
Get:3 http://cdn-fastly.deb.debian.org/debian stretch Release.gpg [2434 B]
Fetched 120 kB in 1s (110 kB/s)