The most convenient way to provide a network device to a guest is to setup a persistent TAP interface on the host. This section will explain how to do this for basic IPv4 connectivity.

sudo ip tuntap add mode tap user $USER vnet_hdr crosvm_tap
sudo ip addr add dev crosvm_tap
sudo ip link set crosvm_tap up

These commands create a TAP interface named crosvm_tap that is accessible to the current user, configure the host to use the IP address, and bring the interface up.

The next step is to make sure that traffic from/to this interface is properly routed:

sudo sysctl net.ipv4.ip_forward=1
# Network interface used to connect to the internet.
HOST_DEV=$(ip route get | awk -- '{printf $5}')
sudo iptables -t nat -A POSTROUTING -o "${HOST_DEV}" -j MASQUERADE
sudo iptables -A FORWARD -i "${HOST_DEV}" -o crosvm_tap -m state --state RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -i crosvm_tap -o "${HOST_DEV}" -j ACCEPT

The interface is now configured and can be used by crosvm:

crosvm run \
  --net tap-name=crosvm_tap \

Provided the guest kernel had support for VIRTIO_NET, the network device should be visible and configurable from the guest:

# Replace with the actual network interface name of the guest
# (use "ip addr" to list the interfaces)
sudo ip addr add dev "${GUEST_DEV}"
sudo ip link set "${GUEST_DEV}" up
sudo ip route add default via
# "" is chosen arbitrarily as a default, please replace with your local (or preferred global)
# DNS provider, which should be visible in `/etc/resolv.conf` on the host.
echo "nameserver" | sudo tee /etc/resolv.conf

These commands assign IP address to the guest, activate the interface, and route all network traffic to the host. The last line also ensures DNS will work.

Please refer to your distribution's documentation for instructions on how to make these settings persistent for the host and guest if desired.