Which statement correctly describes how backbone routers handle private IP addresses?

Which statement correctly describes how backbone routers handle private IP addresses?

• A. They do not allow packets from or to internal IP addresses.
• B. They automatically translate private addresses to public addresses.
• C. They route internal traffic only via NAT.
• D. They block all traffic from internal networks.

Answer: (A)

Private IP addresses are not routable on the public Internet. Backbone routers form the Internet’s core and only forward packets that use globally unique, public addresses. Because private addresses aren’t meant to be reachable across multiple networks, these core routers don’t forward such packets toward other networks. In practice, traffic from a private network to the Internet is handled at the network edge with NAT, which translates private addresses to public ones before the traffic traverses the backbone. That’s why the statement that backbone routers do not allow packets from or to internal IP addresses best describes their handling of private addresses. The other options don’t fit: NAT is typically performed at edge gateways, not by backbone routers; NAT alone isn’t what backbone routing uses to handle internal addresses; and backbone routers don’t block all internal traffic—private addresses simply aren’t routed across the Internet, while legitimate public-address traffic continues to flow.

Private IP addresses are not routable on the public Internet. Backbone routers form the Internet’s core and only forward packets that use globally unique, public addresses. Because private addresses aren’t meant to be reachable across multiple networks, these core routers don’t forward such packets toward other networks. In practice, traffic from a private network to the Internet is handled at the network edge with NAT, which translates private addresses to public ones before the traffic traverses the backbone. That’s why the statement that backbone routers do not allow packets from or to internal IP addresses best describes their handling of private addresses.

The other options don’t fit: NAT is typically performed at edge gateways, not by backbone routers; NAT alone isn’t what backbone routing uses to handle internal addresses; and backbone routers don’t block all internal traffic—private addresses simply aren’t routed across the Internet, while legitimate public-address traffic continues to flow.