addresses and MAC addresses that they see on a regular and repeated basis. This means that a typical device contains mapping information pertaining only to devices on its own network. It knows very little about devices beyond its LAN. Routers build tables that describe all networks connected to them. ARP tables kept by routers can contain IP addresses and MAC addresses of devices located on more than one network. In addition to mapping IP addresses to MAC addresses, router tables also map ports. Can you think of a reason why routers would need to do this? (Note: Examine the router's ARP table below.)Destination NetworkRouter Port201.100.100.0201.100.100.1201.100.101.0201.100.101.1201.100.120.0201.100.120.1201.100.150.0201.100.150.1 What happens if a data packet reaches a router that is destined for a network to which it is not connected? In addition to IP addresses and MAC addresses of devices located on networks to which it connects, a router also possesses IP addresses and MAC addresses of other routers. It uses these addresses to direct data toward its final destination. If a router receives a packet whose destination address is not in its routing table, it forwards it to the address of another router that most likely does contain information about the destination host in its routing table. ARP is used only on a local network. What would happen if a local router wanted to ask a non-local router to provide indirect routing (next-hop) services, but did not know the MAC address of the non-local router? When a router does not know the MAC address of the next-hop router, the source router (router that has the data to be sent on) issues an ARP request. A router that is connected to the same segment as the source router receives the ARP request. This router issues an ARP reply to the router that originated the ARP request. The reply contains the MAC address of the non-local router. A device on one network cannot send an ARP request to a...
