Get list of DHCP clients with KVM+libvirt?
This feature was requested a long time ago. Now libvirt supports it by providing two new commands: domifaddr and net-dhcp-leases
Usage: domifaddr <domain> [interface] [--full] [--source lease|agent]
Example outputs:
virsh # domifaddr f20 --source agent
Name MAC address Protocol Address
-------------------------------------------------------------------------------
lo 00:00:00:00:00:00 ipv4 127.0.0.1/8
- - ipv6 ::1/128
eth0 52:54:00:2e:45:ce ipv4 10.1.33.188/24
- - ipv6 2001:db8:0:f101::2/64
- - ipv6 fe80::5054:ff:fe2e:45ce/64
eth1 52:54:00:b1:70:19 ipv4 192.168.105.201/16
- - ipv4 192.168.201.195/16
- - ipv6 2001:db8:ca2:2:1::bd/128
eth2 52:54:00:36:2a:e5 N/A N/A
eth3 52:54:00:20:70:3d ipv4 192.168.105.240/16
- - ipv6 fe80::5054:ff:fe20:703d/64
virsh # domifaddr f20 --full
Name MAC address Protocol Address
-------------------------------------------------------------------------------
vnet0 52:54:00:2e:45:ce ipv6 2001:db8:0:f101::2/64
vnet1 52:54:00:b1:70:19 ipv4 192.168.105.201/16
vnet1 52:54:00:b1:70:19 ipv6 2001:db8:ca2:2:1::bd/128
vnet3 52:54:00:20:70:3d ipv4 192.168.105.240/16
virsh # domifaddr f20 eth0 --source agent --full
Name MAC address Protocol Address
-------------------------------------------------------------------------------
eth0 52:54:00:2e:45:ce ipv4 10.1.33.188/24
eth0 52:54:00:2e:45:ce ipv6 2001:db8:0:f101::2/128
eth0 52:54:00:2e:45:ce ipv6 fe80::5054:ff:fe2e:45ce/64
For eth0, ipv6 is managed by libvirt, but ipv4 is not.
For eth1, the second IP is created using ip aliasing.
For eth2, there is no IP configured as of yet.
For eth3, only ipv4 has been configured.
fd00::/8 are private ipv6 ranges. Hence not visible through --source lease
In a different scenario:
Example Usage: net-dhcp-leases <network> [mac]
virsh # net-dhcp-leases --network default6
Expiry Time MAC address Protocol IP address Hostname Client ID or DUID
-------------------------------------------------------------------------------------------------------------------
2014-06-16 03:40:14 52:54:00:85:90:e2 ipv4 192.168.150.231/24 fedora20-test 01:52:54:00:85:90:e2
2014-06-16 03:40:17 52:54:00:85:90:e2 ipv6 2001:db8:ca2:2:1::c0/64 fedora20-test 00:04:b1:d8:86:42:e1:6a:aa:cf:d5:86:94:23:6f:94:04:cd
2014-06-16 03:34:42 52:54:00:e8:73:eb ipv4 192.168.150.181/24 ubuntu14-vm -
2014-06-16 03:34:46 52:54:00:e8:73:eb ipv6 2001:db8:ca2:2:1::5b/64 - 00:01:00:01:1b:30:c6:aa:52:54:00:e8:73:eb
libvirt uses dnsmasq to provide DHCP to the guests, so you could trawl /var/log/daemon.log or dig through the leases file in /var/lib/libvirt to get an IP to hostname mapping.