ARP
The Address Resolution Protocol (ARP) determines the MAC address and IP address correspondence for a network device.
A local computer will maintain an ARP cache that is a table of MAC addresses and the corresponding IP addresses. Before a connection with another computer is made, the local computer first checks its ARP cache to determine whether the remote computer has an entry. If it does, the local computer reads the remote computer’s MAC address and writes it into the destination field of the packets to be sent.
If the remote computer does not have an ARP cache entry, the local computer must send an ARP request and wait for a reply.
When the local computer receives the ARP reply packet, the local ARP reads the IP MAC address pair, and then checks the ARP cache for this entry. If there is an entry, it is updated with the new information. If there is no entry, a new entry is made.
There are two possible cases when an ARP packet is received by a local computer. First, the local computer is the target of the request. If it is, the local ARP replies by sending its MAC IP address pair back to the requesting system. Second, if the local computer is not the target of the request, the packet is dropped.
Multicasting
Multicasting is a group of protocols and tools that enable a single source point to send packets to groups of multiple destination points with persistent connections that last for some amount of time. The main advantage to multicasting is a decrease in the network load compared to broadcasting.
Multicast Groups
Class D IP addresses are assigned to a group of network devices that comprise a multicast group. The four most significant four bits of a Class D address are set to “1110”. The following 28 bits is referred to as the ‘multicast group ID’. Some of the range of Class D addresses are registered with the Internet Assigned Numbers Authority (IANA) for special purposes. For example, the block of multicast addresses ranging from 224.0.0.1 to 224.0.0.225 is reserved for use by routing protocols and some other
Figure 5-17. Class D Multicast Address
Some of the reserved IP multicast addresses are as follows:
Address | Assignment |
224.0.0.0Base Address (reserved)
224.0.0.1All Systems on this subnet
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