ysically connected to two or more networks through a number of network interfaces. Figure 4 provides a representation of this.The machine in the middle, the gateway machine, has two network interfaces. One has the IP address 138.77.37.1 and the other 138.77.36.1 (it's common practice for a networks gateway machine to have the host id 1.B) How it worksWhen the machine 138.77.37.37 wants to send some information to the machine 138.77.36.15 it can't just put the data onto the network. The two machines are on separate networks. 138.77.37.37 sends the information to the gateway and "asks" the gateway to forward it onto 138.77.36.15= Figure 4 =A simple gateway4.4 INTERNET ADDRESSES TO HARDWARE ADDRESSESA) Converting Internet To Hardware AddressesNetworking hardware knows nothing about Internet addresses. Hardware general uses its own addressing scheme. It is the responsibility of the network access layer of the TCP/IP protocol stack to map Internet addresses to physical network addresses.Different networking hardware will have different addressing schemes. Therefore this mapping will be performed differently for different hardware.B) Address Resolution ProtocolThe Address Resolution Protocol (ARP) is the protocol that performs the mapping of IP addresses to ethernet addresses. The ARP software on a machine maintains a table that contains the translation between IP address and ethernet address.When the machine wants to send data to a local machine the ARP software is asked if it knows about the IP address. If the ARP table contains the IP address, the ethernet address is returned.If the IP address is not known a packet is broadcast to every host on the local network containing the required IP address. Every host on the network examines the packet. If the receiving host recognises the IP address as its own, it will send a reply back that contains its ethernet address. This response is then placed into the ARP table.The Arp Command :On a UNIX m...
