Question 645 - N10-008 discussion

The best answer is B. Public address on the perimeter router.

Port address translation (PAT) is a function that allows multiple users within a private network to make use of a minimal number of IP addresses. Its basic function is to share a single IP public address between multiple clients who need to use the Internet publicly. It is an extension of network address translation (NAT)1.

PAT works by creating dynamic NAT mapping, in which a global (public) IP address and a unique port number are selected. The router keeps a NAT table entry for every unique combination of the private IP address and port, with translation to the global address and a unique port number2.

Therefore, an organization would use PAT for having a public address on the perimeter router, which can be shared by many hosts on the private network using different port numbers. This can reduce the bandwidth consumption and cost of the organization's internet connection, as well as provide some security benefits by hiding the internal network structure3.

The other options are not correct because:

VLANs on the perimeter are not related to PAT, as they are used to segment the network into logical groups based on different criteria, such as function, security, or performance4.

Non-routable address on the perimeter router would not allow the organization to access the Internet or the cloud, as non-routable addresses are not valid on the public network and cannot be translated by PAT5.

Servers on the perimeter are not a reason to use PAT, as servers usually have static IP addresses and do not need to share a public address with other hosts. Servers on the perimeter may use NAT, but not PAT, to map their private IP addresses to a public IP address2.