now in this setup we will be introduced to the Routes.

Routes define the path that packets take to reach their destination. In networking, a route has two main components:

1. Destination:

   This specifies the target IP range (subnet) or a specific IP address to which the route applies. For example:

   • 192.168.1.0/24 means "any device with an IP address in the range 192.168.1.0 to 192.168.1.255."
   • default means "any IP address that doesn't match other routes in the table."
     • What is "default" in routing?

       • In networking, a default route is like a fallback option. It tells the device:

         "If I don’t have a specific route for where the packet is supposed to go, send it to this gateway (or router)."

         Think of it like this:

         • If you know the exact street address (specific route), you follow the directions.
         • If you don’t know the address, you head to the main road (default route) and let someone there guide you.

2. Gateway:

   This specifies the next hop (typically a router's IP address) where the packet should be forwarded to continue its journey toward the destination.

How it works:

When a host needs to send a packet:

• It checks its routing table to see if there’s a route that matches the destination IP.
• If the destination IP matches a route:
  • The packet is sent to the corresponding gateway (or directly to the destination if no gateway is required).
• If no match is found, the packet is sent to the default gateway (the default route).

So now we should put the ip of the interface r2 as gateway of the route of B1 and since routers are designed to connect different subnets. For traffic to leave the host’s subnet, the router must first receive the packet from the host. If the host and router are in different subnets, the host cannot directly send packets to the router because:

• It assumes the router is unreachable.
• The packet is dropped.

so the interface r2 and b1 should be in the same subnet so they will have the same mask and b1 ip should have the same network bytes of r2

same thing for host a with r1