255.255.255.255 broadcast address meaning

Question

Lets suppose we have a computer with three NICs:

NIC_1: 172.16.1.1/24

NIC_2: 192.168.1.1/24

NIC_3: 103.55.34.32/24

We send a packet with the destination IP address being 255.255.255.255.

1) if the default gw is on the 103.55.34/24 network, will the packet be sent through NIC_3 or will the packet be sent through every NIC?

2) If we make an assumption that the whole internet is a one big network and this network network address is 0.0.0.0/0, the 255.255.255.255 address looks like a broadcast address for the whole network (for the internet), right?

3) What would be the meaning of a network address like this: 1.2.0.0/0? (is this correct and if not, why not)

Answer 1

1. It will be sent through the first interface in the route table that matches the destination, evaluated in the order static route>route>gateway>metric. If you type route print you'll see something similar to the following:

   Network Destination        Netmask          Gateway       Interface  Metric
   [Loads of entries for your various NICs, routes and static routes]
   255.255.255.255  255.255.255.255    103.55.34.254   103.55.34.32       1
   Default Gateway:       103.55.34.254
   

   Indicating that the broadcast/multicast test ping will use your NIC_3

2. Assuming you had a network 0.0.0.0/0, then yes 255.255.255.255 WOULD be the broadcast address. The Internet however is not one big network, it's a series of interconnected completely separate networks (hence inter-net!)