Resource Groups

Resource groups allow you to operate on groups of VMs at once.
A resource can only be part of one group.
You can't nest groups, it is not hierarchial.
But you can link resource into a group, to associate a resource from another group with this group.
No limits to the number of resources in a group.
You can't rename a group.

If want to restrict Azure network traffic through a particular router onto our on-premise network.
Resources tab --> add --> search for: Route table -->create a route table and select the resource group
Associate a virtual network to the Route table we create.
route table settings --> routes --> Add link (Route name, Address prefix,Next hop type(Virtual network gateway(is is a site to site VPN)),)

Next hop type set to "none" means it is a black hole.All the IP Address set traffic will be set to black hole, means traffic is ignored/

Once route entries created, associate a subnet also to the Route table.