What happens to the MAC addresses of packets when they transit across networks? What happens to IP addresses when they move across networks?

How does "network masking" differentiate between host addresses and network addresses in IP?

Can you tell me how many IPv4 addresses there are in total? The lifespan of IPv4 addresses has been extended because to Network Address Translation (NAT) (NAT). Should IPv6 be used universally? Is the use of IPv6 essential to the creation of some cutting-edge technology?

When it comes to modern networks, which routing protocols are preferred both inside and externally?

What is the rationale behind the absence of sequential numbering in ACK packets?

Is it accurate to say that, in the case of routers, packet routing happens at MAC addresses? If you replied no, could you kindly describe the equipment that would be needed to do the job, along with how it functions, and then please explain how it works.

Are routers employing layer-2 protocols that pose difficulties? What is the reason for the persistence of ICMP packets despite modifications to the subnet of a PPP-encapsulated router's serial interface?

Define the term "TCP/IP model" and compare it with the OSI model in terms of layers.