Exam 200-310 topic 2 question 173 discussion

Actual exam question from Cisco's 200-310

Question #: 173
Topic #: 2

HostA is a computer on your company's network. RouterA is a NAT router. HostA sends a packet to HostB, and HostB sends a packet back to HostA.

Which of the following addresses is an outside local address?

A. 15.16.17.18
B. 22.23.24.25
C. 192.168.1.22
D. 192.168.1.30

Show Suggested Answer

Suggested Answer: D 🗳️
Section: Addressing and Routing Protocols in an Existing Network Explanation

The 192.168.1.30 address is an outside local address. An outside local address is an IP address that represents an outside host to the local network. Network
Address Translation (NAT) translates between public and private IP addresses to enable hosts on a privately addressed network to access the Internet. Public addresses are routable on the Internet, and private addresses are routable only on internal networks. Several IP address ranges are reserved for private, internal use; these addresses, shown below, are defined in Request for Comments (RFC) 1918.
✑ 10.0.0.0 through 10.255.255.255
✑ 172.16.0.0 through 172.31.255.255
✑ 192.168.0.0 through 192.168.255.255
The outside local address is often the same as the outside global address, particularly when inside hosts attempt to access resources on the Internet. However, in some configurations, it is necessary to configure a NAT translation that allows a local address on the internal network to identify an outside host. When RouterA receives a packet destined for 192.168.1.30, RouterA translates the 192.168.1.30 outside local address to the 15.16.17.18 outside global address and forwards the packet to its destination. To configure a static outside local-to-outside global IP address translation, you should issue the ip nat outside source static outside- global outside-local command.
In this scenario, 15.16.17.18 is an outside global address. An outside global address is an IP address that represents an outside host to the global network.
Outside global addresses are public IP addresses assigned to an Internet host by the host's operator. The outside global address is usually the address registered with the Domain Name System (DNS) server to map a host's public IP address to a friendly name such as www.mycompany.com.
In this scenario, 192.168.1.22 is an inside local address. An inside local address is an IP address that represents an inside host to the local network. Inside local addresses are typically private IP addresses defined by RFC 1918.
In this scenario, 22.23.24.25 is an inside global address. An inside global address is a publicly routable IP address that is used to represent an inside host to the global network. Inside global IP addresses are typically assigned from a NAT pool on the router. You can issue the ip nat pool command to define a NAT pool. For example, the ip nat pool natpool 22.23.24.11 22.23.24.30 netmask 255.255.255.224 command allocates the IP addresses 22.23.24.11 through 22.23.24.30 to be used as inside global IP addresses. When a NAT router receives a packet destined for the Internet from a local host, it changes the inside local address to an inside global address and forwards the packet to its destination.
In addition to configuring a NAT pool to dynamically translate addresses, you can configure static inside local-to-inside global IP address translations by issuing the ip nat inside source static inside-local inside-global command. This command maps a single inside local address on the local network to a single inside global address on the outside network.
It is important to specify the inside and outside interfaces when you configure a NAT router. To specify an inside interface, you should issue the ip nat inside command from interface configuration mode. To specify an outside interface, you should issue the ip nat outside command from interface configuration mode.
The following graphic depicts the relationship between inside local, inside global, outside local, and outside global addresses: