Computer Math/ Subnetting

Question 1

Computer Mathematics

Answer 1

o Humans count using Base-10 numbers
▪ Decimals
▪ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, …
o Computers and networks do not understand decimal numbers natively
o Process numbers using Base-2 numbers
▪ Binary
▪ 0, 1, 10, 11, …

Question 2

Converting Binary to Decimal

Answer 2

o Use table to convert from binary to decimal
o Each number is a factor of 2
o Starting from the right and go to the left
o Populate the table with the binary digits
o Add up any columns that contain a 1

Question 3

Converting Decimal to Binary

Answer 3

o Use subtraction to convert decimal to binary

Question 4

Subnetting

Answer 4

o Default classful subnet masks are rarely the optimal choice for a subnet size
o Subnets can be modified using subnet masks to create networks that are better
scoped
o Creating a subnet involves borrowing bits from the original host portion and
adding them to the network portion

Question 5

Purpose of Subnets

Answer 5

▪ More efficient use of IP addresses than classful default
▪ Enables separation of networks for security
▪ Enables bandwidth control

Question 6

Subnet Classes

Answer 6

Class A— 255.0.0.0—2^24-2=—–16.777,214 addressess
Class B—–255.255.0.0—–2^16-2=——65,534 addressess
Class C—–255.255.255.0—–2^8-2= ——-254 addresses

Question 7

Classless Interdomain Routing (CIDR)

Answer 7

▪ Instead of advertising multiple individual routes, the routes can be
summarized and advertised as a single route
▪ Used to summarize contiguous networks
● Called route aggregation

Question 8

Variable-Length Subnet Masking (VLSM)

Answer 8

▪ Allows subnets of various sizes to be used
▪ Requires a routing protocol that supports it
● RIPv2, OSPF, IS-IS, EIGRP, and BGP
▪ Basically, it is subnetting subnets
▪ Without VLSM, all subnets would have to be the same size