cisco ccna 4 chapter 5 exam answers

cisco ccna 4 chapter 5 exam answers.When using static address translation, you need to create the translation entries manually. If you have 1000 devices, you need to create 1000 static entries in the address translation table, which is a lot of work. Typically, static translation is used to allow external users to access internal resources. To enable internal users to access external resources, dynamic translation is usually used; in this case, the global address assigned to the internal user is less important because the external devices are not directly connected to the internal user; they only return traffic requested by the internal user.When using dynamic NAT, two sets of addresses must be manually specified on the address translation device: one set of internal addresses to be translated (local addresses) and another set of addresses to be translated to (global addresses). When an internal user sends traffic outbound through the address translation device (assumed to be a router), the router compares the source IP address with the internal local address pool. If it is found to be in it, it then decides which internal global address pool to use for the conversion. Next, the router dynamically selects an address in the global address pool that is not currently assigned to an internal device. The router then adds the entry to the address translation table, translates the packet, and sends the packet out again. If the source IP address does not appear in the local address pool, it is not converted and the packet is forwarded out unchanged.When the returned traffic reaches the internal network, the address translation device compares the destination IP address with the address translation table. If a matching entry is found, the global internal address in the destination IP address field of the packet header is converted to a local internal address and the packet is forwarded to the internal network.A dynamic NAT conversion entry is added to the conversion table when the source IP address matches the dynamic NAT policy configuration, and it is removed from the conversion table when the idle timer expires. The same translation is done for the source IP address for all traffic from the same source device, regardless of how many connections the source device has open.22.2.3 Port Address TranslationOne problem with static and dynamic NAT is that only one-to-one address translation is possible. If there are 5000 internal devices using private addresses, and these devices are to connect to the Internet at the same time, then the internal global address pool must have 5000 public addresses. If there are only 1000 public addresses, only the first 1000 devices will be converted, and the other 4000 devices will not be able to access the external target device. To overcome this problem, address reloading can be used, a technique known by many other names, such as Port Address Translation (PAT) and Network Address Port Translation (NAPT).Dynamic PAT translation entries are added to the translation table when a new connection matches the dynamic PAT policy configuration, and such entries are deleted when the idle timer expires or the connection ends. For example, for TCP,the connection will end when the data segment messages FIN and FIN-ACK are seen or when a hard reset (RST) is performed. Most conversion devices are smart enough to use the same PAT address for multiple connections to the same destination device. For example, when downloading web pages from a web server, it is common for dozens of connections to be established. In this case, most conversion devices (including Cisco IOS devices) will convert the source addresses of these connections to the same address. This lets the target server know that these connections are all originating from the same source device.PAT (dynamic NAT address reloading) allows you to use the same global IP address for all internal devices, while usingChapter 22 Address Translation 589the source port in the TCP/UDP message^ header (possibly modifying such a port) to distinguish between connections initiated by different devices. Dynamic NAT address reloading is used in situations where more devices need to access the Internet than the public IP address assigned to you by the ISP.