Internet lost after adding br0 to interface setting in ubuntu

Thanks in advance.

I am trying to install KVM and want to run virt-manager for which i need a bridge to connect with it. After editing bridge in interface file the file looks like below.

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

auto br0
iface br0 inet static
         address 10.18.44.26
         netmask 255.255.255.192
         broadcast 10.18.44.63
         dns-nameservers 10.0.80.11 10.0.80.12
         # set static route for LAN
         post-up route add -net 10.0.0.0 netmask 255.0.0.0 gw 10.18.44.1
         post-up route add -net 161.26.0.0 netmask 255.255.0.0 gw 10.18.44.1
         bridge_ports eth0
         bridge_stp off
         bridge_fd 0
         bridge_maxwait 0
 
# br1 setup with static wan IPv4 with ISP router as a default gateway
auto br1
iface br1 inet static
         address 208.43.222.51
         netmask 255.255.255.248
         broadcast 208.43.222.55
         gateway 208.43.222.49
         bridge_ports eth1
         bridge_stp off
         bridge_fd 0
         bridge_maxwait 0

The problem is after running "sudo systemctl restart network" command i am able to add the bridge but i am losing my internet connection.

kindly help.

Note: I do not understand much about such networking things like IP, gateway, netmask. I have started learning the things recently. So kindly elaborate your answer with networking basics. I would be really grateful.