NAT Operation on Cisco Routers
When a packet leaves an inside network, NAT translates the inside address to a unique InterNIC address for use on the outside network, as shown in Figure 5.5. The router in Figure 5.5 will be configured for an address translation and will maintain a NAT table. When the packet returns from the outside network, the NAT router will again perform an address translation from the valid InterNIC address to a local inside address. Inside global IP address assigned by InterNIC, 131.108.1.1 24 Inside...
IP Addressing Review
The network layer addressing used by IP is a field 32 bits in length and represented in a dotted decimal format, such as 10.99.34.50. IP addresses have three defined portions a network portion, a host portion, and a subnet mask. A subnet mask (also a 32-bit field) is used to identify and distinguish between the network and host portions, as discussed later in this chapter. Figure 5.2 demonstrates a typical network address, using a Class A IP address. In Figure 5.2, the number 10 represents a...
ARP and RARP
Address Resolution Protocol (ARP) and Reverse Resolution Protocol (RARP) carry out important functions in the TCP IP model, which allows devices to communicate at layer 2 of the OSI model. Remember, all frames are sent to a valid MAC address. So, before one IP host can communicate with another, the source device must have an identified layer 2 address to traverse the physical medium or use broadcast frames to locate resources on any particular physical media. ARP is used when a source device...