Network manager is running.

$ sudo iptables -nL
Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0           udp dpt:53 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:53 
ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0           udp dpt:67 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:67 
ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0           udp dpt:53 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:53 
ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0           udp dpt:67 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:67 

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     all  --  0.0.0.0/0            192.168.233.0/24    state RELATED,ESTABLISHED 
ACCEPT     all  --  192.168.233.0/24     0.0.0.0/0           
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           
REJECT     all  --  0.0.0.0/0            0.0.0.0/0           reject-with icmp-port-unreachable 
REJECT     all  --  0.0.0.0/0            0.0.0.0/0           reject-with icmp-port-unreachable 
ACCEPT     all  --  0.0.0.0/0            192.168.122.0/24    state RELATED,ESTABLISHED 
ACCEPT     all  --  192.168.122.0/24     0.0.0.0/0           
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           
REJECT     all  --  0.0.0.0/0            0.0.0.0/0           reject-with icmp-port-unreachable 
REJECT     all  --  0.0.0.0/0            0.0.0.0/0           reject-with icmp-port-unreachable 

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

$ sudo iptables -nL -t nat
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination         
MASQUERADE  tcp  --  192.168.233.0/24    !192.168.233.0/24    masq ports: 1024-65535 
MASQUERADE  udp  --  192.168.233.0/24    !192.168.233.0/24    masq ports: 1024-65535 
MASQUERADE  all  --  192.168.233.0/24    !192.168.233.0/24    
MASQUERADE  tcp  --  192.168.122.0/24    !192.168.122.0/24    masq ports: 1024-65535 
MASQUERADE  udp  --  192.168.122.0/24    !192.168.122.0/24    masq ports: 1024-65535 
MASQUERADE  all  --  192.168.122.0/24    !192.168.122.0/24    

$ cat /etc/network/interfaces
auto lo
iface lo inet loopback

Two guests: 179 was shutdown, 110 froze.

Before:
$ cat /proc/net/arp
IP address       HW type     Flags       HW address            Mask     Device
192.168.242.1    0x1         0x2         00:12:17:1a:50:47     *        eth0
192.168.122.110  0x1         0x2         52:54:00:a2:4e:07     *        virbr0
192.168.122.179  0x1         0x2         52:54:00:72:58:e3     *        virbr0

While the freeze:
$ cat /proc/net/arp
IP address       HW type     Flags       HW address            Mask     Device
192.168.242.1    0x1         0x2         00:12:17:1a:50:47     *        eth0
192.168.122.110  0x1         0x2         52:54:00:a2:4e:07     *        virbr0
192.168.122.179  0x1         0x2         52:54:00:72:58:e3     *        virbr0

Just after the freeze stopped:
$ cat /proc/net/arp
IP address       HW type     Flags       HW address            Mask     Device
192.168.242.1    0x1         0x2         00:12:17:1a:50:47     *        eth0
192.168.122.110  0x1         0x2         52:54:00:a2:4e:07     *        virbr0
192.168.122.179  0x1         0x2         52:54:00:72:58:e3     *        virbr0

Some time after the freeze stop (guess: ~30 seconds):
$ cat /proc/net/arp
IP address       HW type     Flags       HW address            Mask     Device
192.168.242.1    0x1         0x2         00:12:17:1a:50:47     *        eth0
192.168.122.110  0x1         0x2         52:54:00:a2:4e:07     *        virbr0