https://kashyapc.fedorapeople.org/virt/add-network-card-in-guest.txt
Add a second NIC for a libvirt guest
====================================
Purpose: attach a new libvirt network to a live guest -- this takes
effect immediately, and the NIC will be persistent on further reboots.
(0) Before adding a NIC, enumerate the network interfaces for vm1:
$ virsh domiflist vm1
Interface Type Source Model MAC
-------------------------------------------------------
vnet0 network default virtio 52:54:00:cd:58:29
(1) Let's add a new NIC for the guest (the MAC address was chosen
randomly):
$ virsh attach-interface --domain vm1 --type network
--source openstackvms --model virtio
--mac 52:54:00:4b:73:5f --config --live
Interface attached successfully
(2) Now again, enumerate the network interfaces for vm1, invoke the
below command on the host:
$ virsh domiflist vm1
Interface Type Source Model MAC
-------------------------------------------------------
vnet0 network default virtio 52:54:00:cd:58:29
vnet1 network openstackvms virtio 52:54:00:4b:73:5f
(3) Inside the guest, you can see the second interface is now available:
$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default
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 pfifo_fast state UP group default qlen 1000
link/ether 52:54:00:cd:58:29 brd ff:ff:ff:ff:ff:ff
inet 192.168.122.50/24 brd 192.168.122.255 scope global dynamic eth0
valid_lft 2397sec preferred_lft 2397sec
inet6 fe80::5054:ff:fecd:5829/64 scope link
valid_lft forever preferred_lft forever
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 52:54:00:4b:73:5f brd ff:ff:ff:ff:ff:ff
inet 192.169.142.233/24 brd 192.169.142.255 scope global dynamic eth1
valid_lft 3226sec preferred_lft 3226sec
inet6 fe80::5054:ff:fe4b:735f/64 scope link
valid_lft forever preferred_lft forever
To detach the NIC
-----------------
(1) If you want to detach the network interface, this will take effect on
next boot of the guest:
$ virsh detach-interface --domain vm1 --type network
--mac 52:53:00:4b:75:6f --config
Interface detached successfully
(2) Reboot the guest, and enumerate the network interfaces for vm1:
$ virsh domiflist vm1
Interface Type Source Model MAC
-------------------------------------------------------
vnet0 network default virtio 52:54:00:cd:58:29
(3) And, inside vm1, you can now see only see the interface for
associated with the default network:
$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default
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 pfifo_fast state UP group default qlen 1000
link/ether 52:54:00:cd:58:29 brd ff:ff:ff:ff:ff:ff
inet 192.168.122.50/24 brd 192.168.122.255 scope global dynamic eth0
valid_lft 3600sec preferred_lft 3600sec
inet6 fe80::5054:ff:fecd:5829/64 scope link
valid_lft forever preferred_lft forever
NOTES:
- While detaching, using the "--live" parameter is not recommended as
it might affect any existing network activities on the NIC to be
removed.
- If detaching the NIC doesn't go as expected or it still shows up, to
get the guest back to its previous networking state, edit the guest
XML:
$ virsh edit vm1
[. . .]
and remove the network interface attribute:
<interface type='network'>
<mac address='52:54:00:4b:74:6f'/>
<source network='testnw'/>
<model type='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
</interface>