solve the "no network with matching name 'default'" problem.

solve the "no network with matching name 'default'" problem.

# virsh create rhel7.xml 
error: Failed to create domain from rhel7.xml
error: Network not found: no network with matching name 'default'

# virsh net-list --all
 Name                 State      Autostart     Persistent
----------------------------------------------------------
 default              active     no            yes

# virsh net-define /dev/stdin <<EOF
> <network connections='1'>
>   <name>default</name>
>   <uuid>18bb3790-11ee-41b1-8847-970590a06e4d</uuid>
>   <forward mode='nat'/>
>   <bridge name='virbr0' stp='on' delay='0' />
>   <mac address='52:54:00:F6:C8:DE'/>
>   <ip address='192.168.122.1' netmask='255.255.255.0'>
>     <dhcp>
>       <range start='192.168.122.2' end='192.168.122.254' />
>     </dhcp>
>   </ip>
> </network>
> EOF
Network default defined from /dev/stdin

# virsh net-start default
Network default started

# virsh net-list --all
 Name                 State      Autostart     Persistent
----------------------------------------------------------
 default              active     no            yes

# virsh create rhel7.xml 
Domain rhel7 created from rhel7.xml

# virsh list
 Id    Name                           State
----------------------------------------------------
 15    rhel7                          running

##############################################################
# ifconfig virbr0 down
# virsh net-start default
error: Failed to start network default
error: Unable to create bridge virbr0: File exists

# ifconfig virbr0 up
# virsh net-start default
error: Failed to start network default
error: internal error: Network is already in use by interface virbr0

# ifconfig virbr0 down
# brctl delbr virbr0
# virsh net-autostart default
Network default marked as autostarted
# virsh net-start default
Network default started

Damn thank you so much