Identifying a Local or Remote Network

With every packet that is sent across a network, the big question is: Is the destination address local or remote? The destination is local if the network portion of the source's IP address is the same as that of the destination's IP address.

If any bits of the network portions differ from each other, then the destination is remote. This is similar to figuring out whether someone lives on the same street as you do. If you look at the person's street name and it is the same as yours, the person lives on the same street as you do. If any part of the street name is different, the person is remote to your street. But, as stated earlier, before IP can figure out whether the destination address is remote, IP has to determine how many bits are in the network portion of the source IP address. IP uses the subnet mask to determine which bits of the IP address represent the network portion of the address.

The subnet mask is 32 bits long, but you use dotted decimal notation to represent it, just as you do with an IP address. A subnet mask, in binary, is made up of several contiguous 1s, which represent the network portion of the address, and then the rest of the bits are 0s. When determining how many of the 32 bits are in the network portion of an IP address, IP looks at the subnet mask for the contiguous 1s.

Dotted decimal notation: The decimal representation of an IP address or subnet mask. Four decimal numbers separated by periods (or dots) is the preferred way to represent an address or mask. When you look at a subnet mask in binary, imagine that the 1s represent the beginning and
End of an area code. The number of bits set to 1 in the subnet mask is the number of bits that will be compared to determine if the destination is local or remote. This is similar to evaluating two telephone numbers by comparing the values that are inside the parentheses.

The 1s in the subnet mask will act like the number of digits within the parentheses in an area code; these are the only values that are compared to determine if the destination is local or remote. When someone gives you their telephone number, you can tell if it is a long distance number just by looking at the digits in the parentheses. Likewise, the subnet mask's only purpose is to determine how many bits are used to identify if the destination host of every packet is local or remote.

For example, if the first 16 bits are set to 1, then IP compares the first 16 bits of the source IP address with the first 16 bits of the destination IP address. If these 16 bits are exactly the same, the destination host is local; if any of the bits are different, the destination host is remote. If the first 24 bits are set to 1, then IP compares the first 24 bits of the source IP address with the first 24 bits of the destination IP address. If these 24 bits are exactly the same, the destination host is local; if any of the bits are different, the destination host is remote.

BIO:
Brents Lyons is an IT professional from Exam key. Are you really looking for this comptia a+ 220-801 exam assistance? Move ahead to take the benefit of comptia 220-802  and pass your exam easily .