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+--------+ |Hardware| 2 bytes |MAC | |Address | |Type | +--------+ |Protocol| 2 bytes |Address | |Type | +--------+ |Hardware| 1 byte |MAC | |Address | |Size | +--------+ |Protocol| 1 byte |Address | |Size | +--------+ |Op | 2 bytes +--------+ |Sender | 6 bytes (depends on the above size field) |MAC | |Address | +--------+ |Sender | 4 bytes (depends on the above size field) |IP | |Address | +--------+ |Target | 6 bytes (depends on the above size field) |MAC | |Address | +--------+ |Target | 4 bytes (depends on the above size field) |IP | |Address | +--------+The fields are further explained below: +---------+-------------------------------------------------------+ |Ethernet |For a ARP request, source MAC address is the MAC | |Header |address of the host sending the ARP request, | | |destination MAC address is the Ethernet broadcast | | |address (FF:FF:FF:FF:FF:FF), frame type field is 0x806.| | |For ARP reply, source MAC address is the MAC address of| | |the host replying to the ARP request, destination MAC | | |address is the MAC address of the host that sent the | | |ARP request, and the frame type field is 0x806. | +---------+-------------------------------------------------------+ |Hardware |Type of the hardware MAC address which is being mapped.| |Address |For Ethernet the value of this field is 1. | |Type | | +---------+-------------------------------------------------------+ |Protocol |Type of the protocol address to which the MAC address | |Address |is mapped. For IP address the value of this field is | |Type |0x800. | +---------+-------------------------------------------------------+ |Hardware |Size of the hardware MAC address. For Ethernet, the | |Address |value of this field is 6. | |Size | | +---------+-------------------------------------------------------+ |Protocol |Size of the protocol address. For IP, the value of | |Address |this field is 4. | |Size | | +---------+-------------------------------------------------------+ |Operation|Type of operation being performed. The value of this | | |field can be 1 (ARP request), 2 (ARP reply) | +---------+-------------------------------------------------------+ |Source |The hardware MAC address of the host sending the ARP | |MAC |request or reply. This is same as the source MAC | |address |address present in the Ethernet header. | +---------+-------------------------------------------------------+ |Source |The IP address of the host sending the ARP request or | |IP |reply. | |address | | +---------+-------------------------------------------------------+ |Target |The hardware MAC address of the host receiving the ARP | |MAC |request or reply. This is same as the destination MAC | |address |address present in the Ethernet header. | +---------+-------------------------------------------------------+ |Target |The IP address of the host receiving the ARP request | |IP |or reply. | |address | | +---------+-------------------------------------------------------+
When a host sends a packet How does it determine if the destination of the packet is on the same local network or on a remote network?When a router receives a packet, the router checks its routing table to determine if the destination address is for a system on one of it's attached networks or if the message must be forwarded through another router. It then sends the message to the next system in the path to the destination.
When a host receives a packet How does it know which process to send the packet to?When the packet arrives on the receiving host, the packet travels through the TCP/IP protocol stack in the reverse order from which it was sent. Figure 1–1 illustrates this path. Moreover, each protocol on the receiving host strips off header information that is attached to the packet by its peer on the sending host.
Which interface is used when a host sends a packet to a device on another network?Routing - The network layer provides services to direct packets to a destination host on another network. To travel to other networks, the packet must be processed by a router.
Where does a host send packets when sending to a destination address outside of its network?In cases where hosts are local, they can communicate directly. In cases where the destination host is on a different network, the packets must be sent to a router (Gateway), who will then forward them along on their journey to the destination network.
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