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Creating new VM network

Create an the xml for an isolated network:​

/tmp/VMswitch.xml
<network>
 <name>VMnetwork</name>
 <bridge name="VMnetwork"/>
 <ip address="172.16.0.1" netmask="255.255.0.0"/>
</network>

Define the new network:​

virsh
net-define /tmp/vmswitch.xml
#Network VMnetwork defined from /tmp/vmswitch.xml
net-autostart VMnetwork
#Network VMnetwork marked as autostarted
net-start VMnetwork
#Network VMnetwork started

Change a VM network​

Get current interfaces​

virsh
domiflist dns-dhcp

Attach a new interface​

virsh attach-interface \
     --domain dns-dhcp \
     --type network \
     --source VMnetwork \
     --model virtio \
     --config

Detach old interface​

virsh
destroy dns-dhcp
detach-interface --domain dns-dhcp --type bridge --mac 52:54:00:8a:92:ea --config

Start the VM again:

virsh
start dns-dhcp

Troubleshooting​

Setting static IP address for a new interface​

You may need to create the interface within network-scripts/ after adding an interface on the hypervisor. This can be easily scripts, as follows:

~/set-new-nic.sh
#!/bin/bash
#finds name of new interface, creates ifcfg file if need-be, then populates with parameters
interface=`ls /sys/class/net | grep -v lo`
ifcfg_file=`ls /etc/sysconfig/network-scripts | grep ifcfg-$interface`

if [ -z "${ifcfg_file}" ]; then
     echo "==> ifcfg-${interface} does not exist, creating now..."
     read -p "Enter IP address: " ip_addr
     read -p "Enter network mask: " net_mask
     read -p "Enter network ID: " net_work
     read -p "Enter broadcast: " broad_cast
     read -p "Enter gateway: " gate_way
     mac_addr=`ip addr show $interface | awk 'FNR == 2 {print $2}'`

     read -p "Enter DNS server (leave blank for self): " dns_svr
     if [ -z "${dns_svr}" ]; then
          echo "==> Setting DNS server to 127.0.0.1"
          dns_svr="127.0.0.1"
     fi

     tee /etc/sysconfig/network-scripts/ifcfg-$interface << EOF > /dev/null
DEVICE=$interface
HWADDR=$mac_addr
BOOTPROTO=static
ONBOOT="yes"
IPADDR=$ip_addr
NETMASK=$net_mask
NETWORK=$net_work
BROADCAST=$broad_cast
DNS1=$dns_svr
GATEWAY=$gate_way
EOF
echo "==> ifcfg-${interface} has been created."
else
     echo "${ifcfg_file} exists, check the directory /etc/sysconfig/network-scripts"
fi
tip

The original network-scripts/ifcfg-eth0 file can (and probably should) be deleted.

Machine networking may need to be restarted​

After setting the IP the machine's network service may need to be restarted once or twice for the IP to take affect.

Source​