CCNA 2 v6 RSE Chapter 9 Exam Online

Hint

NAT was developed to conserve IPv4 addresses. A side benefit is that NAT adds a small level of security by hiding the internal network addressing scheme. However, there are some drawbacks of using NAT. It does not allow true peer-to-peer communication and it adds latency to outbound connections.

Hint

A PAT-enabled router maintains a table that consists of a mapping of inside local IP addresses and TCP/UDP port numbers to outside local addresses and TCP/UDP port numbers. When traffic returns to the router from the public network, the router would compare the destination port to the PAT mapping table to determine to which inside host the traffic should be sent.

Hint

Port Address Translation is also known as NAT overloading. PAT uses ports as an additional parameter to provide a multiplier effect, making it possible to reuse any one of the 10 inside global addresses up to 65,536 times.

Hint

Many Internet protocols and applications depend on end-to-end addressing from the source to the destination. Because parts of the header of the IP packets are modified, the router needs to alter the checksum of the IPv4 packets. Using a single public IP address allows for the conservation of legally registered IP addressing schemes. If an addressing scheme needs to be modified, it is cheaper to use private IP addresses.

Hint

IPv4 NAT provides some benefits:
– NAT conserves the legally registered addressing scheme.
– NAT increases the flexibility of connections to the public network.
– NAT provides consistency for internal network addressing schemes.
– NAT provides certain level of network security by hiding the internal network topology and hosts.

IPv4 NAT also brings some disadvantages:
– NAT may impact the network performance due to the translation process
– End-to-end addressing is lost, especially when dynamic NAT is used.
– End-to-end IPv4 traceability is also lost.
– NAT complicates tunneling protocols, such as IPsec.
– Services that require the initiation of TCP connections from the outside network, or stateless protocols, such as those using UDP, can be disrupted.

Hint

Interface S0/0/0 should be identified as the outside NAT interface. The command to do this would be R2(config-if)# ip nat outside.

Hint

In order for the ip nat inside source list 4 pool corp command to work, the following procedure needs to be used beforehand:Create an access list that defines the private IP addresses affected by NAT.
Establish a NAT pool of starting and ending public IP addresses by using the ip nat pool command.
Use the ip nat inside source list command to associate the access list with the NAT pool.
Apply NAT to internal and external interfaces by using the ip nat inside and ip nat outside commands.

Hint

If all the addresses in the NAT pool have been used, a device must wait for an available address before it can access the outside network.

Hint

Dynamic NAT uses a pool of inside global addresses that are assigned to outgoing sessions. Creating the pool of inside global addresses is accomplished using the ip nat pool command.

Hint

The overload option enables PAT for a pool of public IP addresses. The source list 4 part of the command refers to the access list that defines what private addresses get translated. The pool corp part of the command refers to the named NAT pool that is created using the separate ip nat pool corp command.

Hint

The steps that are required to configure PAT are to define a pool of global addresses to be used for overload translation, to configure source translation by using the keywords interface and overload, and to identify the interfaces that are involved in the PAT.

Hint

Port Address Translation (PAT) tracks IP flows of internal hosts using port numbers. By using port numbers to track flows, PAT allows many users to share a single public IPv4 address.

Hint

Port forwarding allows a user or program from outside to reach services inside a private network. It is not a technique that allows for using services with nonstandard port numbers. NAT or PAT convert inside IP addresses to outside local addresses.

Hint

The IOS command for port forwarding configuration in global configuration mode is as follows:

ip nat inside source {static {tcp | udp local-ip local-port global-ip global-port}

Where local-ip is the inside local address, local-port is the port on which the web server listens.

Hint

Link-local addresses are defined in RFC 3927. Unique local addresses are independent of any ISP, and are not meant to improve the security of IPv6 networks.

Hint

IPv6 ULAs are unique local addresses. ULAs are similar to IPv4 private IP addresses and are not routable on the Internet. ULAs do not conserve IPv6 addresses. ULAs have a network prefix in the fc00::/7 range.

Hint

The output shows that there are two inside global addresses that are the same but that have different port numbers. The only time port numbers are displayed is when PAT is being used. The same output would be indicative of PAT that uses an address pool. PAT with an address pool is appropriate when more than 4,000 simultaneous translations are needed by the company.

Hint

The translation of the IP addresses from 209.65.200.254 to 192.168.10.10 will take place when the reply comes back from the server.