Subnet Masks Flashcards
128
10000000
255
11111111
252
11111100
11111110
254
11110000
240
11000000
192
10000000
128
11100000
224
248
11111000
11111111
255
192
11000000
224
11100000
240
11110000
11111000
248
254
11111110
What is the broadcast address?
The broadcast address is the last address in the subnet, where all host bits are set to 1.
What is a network address in a subnet?
Network Address – The first address in the subnet, used to identify the network (e.g., 205.68.246.0/24)
What is the gateway address?
The gateway address is the IP address of a router that serves as the exit point for a network, enabling communication between different networks or subnets. It is typically the first or last usable IP address in a subnet (e.g., 205.68.246.1/24). Hosts use the gateway to send data outside their local network.
Explain subnetting and its relationship with the number of hosts.
How do you calculate the number of subnets created when extending a subnet mask beyond /24?
• Use the formula: 2^{(N - 24)} , where N is the new subnet mask. Each added subnet bit doubles the number of subnets.
What formula determines the number of usable hosts per subnet, and why do we subtract two from the total?
The formula is 2^{(32 - N)} - 2 , where N is the subnet mask. We subtract 2 because the first address is reserved for the network address and the last for the broadcast address.
Why is a /30 subnet commonly used for point-to-point links, and what makes /31 a special case?
A /30 subnet provides 2 usable IPs, which is ideal for connecting two devices in a point-to-point link. A /31 subnet is a special case where both addresses can be used, eliminating the need for a network and broadcast address, making it efficient for point-to-point links.
How does adding subnet bits affect the number of available hosts in each subnet?
Adding 1 subnet bit halves the number of available hosts, since more bits are used for subnetting, leaving fewer for host addressing.
What is the relationship between subnet masks, subnet bits, and the number of subnets created?
The more subnet bits added (increasing the subnet mask), the more subnets are created, but each subnet has fewer host addresses available. The trade-off is between network segmentation and host capacity per subnet.
What is /32 used for?
A /32 subnet is used to identify a single host rather than a network. It provides only one IP address with no room for additional hosts.
Common Uses of /32:
1. Loopback Addresses – Assigned to a router’s loopback interface for management and routing processes.
2. Routing Table Entries – Used in routing protocols (e.g., OSPF, BGP) to specify a single IP route.
3. Access Control Lists (ACLs) – Helps define rules for specific devices in firewall and security settings.
4. Point-to-Point Links (Some Cases) – Occasionally used in certain configurations where no network/broadcast addresses are needed.
Since there are no network or broadcast addresses in a /32, it is ideal for uniquely identifying and managing individual devices.
11111100
252
