Subnetting Flashcards
(7 cards)
1
Q
What is subnetting?
A
- Subnetting is the process of dividing a single address block into multiple logical networks
- Each network can then be assigned to different department or functional group
- The more subnets the address block is divided into, the smaller each subnet gets, the lesser hosts addresses that can be assigned
1
Q
How to do subnetting with Fixed Length Subnet Mask?
A
- To do subnetting, we “borrow” bits from the Host portion of the IP address block
- The “borrowed bits” become part of the Network portion
- The number of bits to be “borrowed”, m, depends on the number of subnets to be created where 2^m ≥ Number of subnets required
2
Q
How to count number of subnets?
A
- Count the amount of small networks
- Count the interconnections between routers
3
Q
What is the limitations of using a Fixed-Limit Subnet Mask?
A
- The subnetting example and exercise assume that each subnet has equal number of hosts
- But in reality, some subnets need to support more hosts, while some subnets needs very few host addresses
- Results in unused ip addresses and is wasteful
4
Q
What is Variable-Limit Subnet Mask?
A
VLSM allows to divide an IP address block into subnets of different sizes ie define subnets according to the host counts, and hence avoiding wasting large numbers of addresses as in FLSM
5
Q
How to do subnetting with Variable-Limit Subnet Mask?
A
- Re-order the subnets according to number of host addresses needed, in descending order (ie highest number first)
- For each subnet, calculate the number bits needed in the host portion, n, such that (2^n - 2) ≥ number of host addresses needed
- Allocate a block of 2^n IP addresses to that subnet. Reserve the first IP address as the Network ID, and last IP address as the Broadcast Address. The rest are valid host addresses
- Repeat Step 3 for each subnet, with an IP address block starting immediately after the Broadcast Address of the previous subnet
6
Q
A
