100.97.216.0/21

Public

Class A — /21 prefix — 2,046 usable hosts

Network Address

100.97.216.0

Broadcast Address

100.97.223.255

Subnet Mask

255.255.248.0

Usable Hosts

2,046

First Usable IP

100.97.216.1

Last Usable IP

100.97.223.254

Total IPs

2,048

Prefix Length

/21

Network address — the base address of the block (100.97.216.0). All devices in this subnet share this prefix. Cannot be assigned to a host.

Broadcast address — packets sent to 100.97.223.255 are delivered to every device in the subnet. Also reserved — not assignable.

Usable hosts — the 2,046 addresses between those two that you can assign to servers, VMs, or interfaces.

Subnet mask — 255.255.248.0 is the dotted-decimal equivalent of /21. Older tools and Cisco configs use this format instead of CIDR slash notation.

Full Details

CIDR Notation	100.97.216.0/21
Network Address	100.97.216.0
Broadcast Address	100.97.223.255
Subnet Mask	255.255.248.0
Wildcard Mask	0.0.7.255
Prefix Length	/21
IP Address Class	Class A
Total IP Addresses	2,048
Usable Host Addresses	2,046
First Usable IP	100.97.216.1
Last Usable IP	100.97.223.254
Network (Hex)	0x6461D800
Broadcast (Hex)	0x6461DFFF
Address Type	Public / Globally Routable

Binary Representation

Network Address

01100100.01100001 01100100.01100001.11011000.00000000

Subnet Mask

11111111.11111111.11111000.00000000

The first 21 bits (1s in the mask) identify the network. The remaining 11 bits identify hosts within the network.

Split into Equal Subnets

Split 100.97.216.0/21 into 2 equal /22 subnets (1,022 usable hosts each).

#	CIDR	Network	First Usable	Last Usable	Broadcast	Hosts
1	100.97.216.0/22	100.97.216.0	100.97.216.1	100.97.219.254	100.97.219.255	1,022
2	100.97.220.0/22	100.97.220.0	100.97.220.1	100.97.223.254	100.97.223.255	1,022

Split 100.97.216.0/21 into 4 equal /23 subnets (510 usable hosts each).

#	CIDR	Network	First Usable	Last Usable	Broadcast	Hosts
1	100.97.216.0/23	100.97.216.0	100.97.216.1	100.97.217.254	100.97.217.255	510
2	100.97.218.0/23	100.97.218.0	100.97.218.1	100.97.219.254	100.97.219.255	510
3	100.97.220.0/23	100.97.220.0	100.97.220.1	100.97.221.254	100.97.221.255	510
4	100.97.222.0/23	100.97.222.0	100.97.222.1	100.97.223.254	100.97.223.255	510

Split 100.97.216.0/21 into 8 equal /24 subnets (254 usable hosts each).

#	CIDR	Network	First Usable	Last Usable	Broadcast	Hosts
1	100.97.216.0/24	100.97.216.0	100.97.216.1	100.97.216.254	100.97.216.255	254
2	100.97.217.0/24	100.97.217.0	100.97.217.1	100.97.217.254	100.97.217.255	254
3	100.97.218.0/24	100.97.218.0	100.97.218.1	100.97.218.254	100.97.218.255	254
4	100.97.219.0/24	100.97.219.0	100.97.219.1	100.97.219.254	100.97.219.255	254
5	100.97.220.0/24	100.97.220.0	100.97.220.1	100.97.220.254	100.97.220.255	254
6	100.97.221.0/24	100.97.221.0	100.97.221.1	100.97.221.254	100.97.221.255	254
7	100.97.222.0/24	100.97.222.0	100.97.222.1	100.97.222.254	100.97.222.255	254
8	100.97.223.0/24	100.97.223.0	100.97.223.1	100.97.223.254	100.97.223.255	254

Split 100.97.216.0/21 into 16 equal /25 subnets (126 usable hosts each).

#	CIDR	Network	First Usable	Last Usable	Broadcast	Hosts
1	100.97.216.0/25	100.97.216.0	100.97.216.1	100.97.216.126	100.97.216.127	126
2	100.97.216.128/25	100.97.216.128	100.97.216.129	100.97.216.254	100.97.216.255	126
3	100.97.217.0/25	100.97.217.0	100.97.217.1	100.97.217.126	100.97.217.127	126
4	100.97.217.128/25	100.97.217.128	100.97.217.129	100.97.217.254	100.97.217.255	126
5	100.97.218.0/25	100.97.218.0	100.97.218.1	100.97.218.126	100.97.218.127	126
6	100.97.218.128/25	100.97.218.128	100.97.218.129	100.97.218.254	100.97.218.255	126
7	100.97.219.0/25	100.97.219.0	100.97.219.1	100.97.219.126	100.97.219.127	126
8	100.97.219.128/25	100.97.219.128	100.97.219.129	100.97.219.254	100.97.219.255	126
9	100.97.220.0/25	100.97.220.0	100.97.220.1	100.97.220.126	100.97.220.127	126
10	100.97.220.128/25	100.97.220.128	100.97.220.129	100.97.220.254	100.97.220.255	126
11	100.97.221.0/25	100.97.221.0	100.97.221.1	100.97.221.126	100.97.221.127	126
12	100.97.221.128/25	100.97.221.128	100.97.221.129	100.97.221.254	100.97.221.255	126
13	100.97.222.0/25	100.97.222.0	100.97.222.1	100.97.222.126	100.97.222.127	126
14	100.97.222.128/25	100.97.222.128	100.97.222.129	100.97.222.254	100.97.222.255	126
15	100.97.223.0/25	100.97.223.0	100.97.223.1	100.97.223.126	100.97.223.127	126
16	100.97.223.128/25	100.97.223.128	100.97.223.129	100.97.223.254	100.97.223.255	126

/21 Subnet Reference

Total IPs 2,048

Usable Hosts 2,046

Subnet Mask 255.255.248.0

Wildcard 0.0.7.255

Full /21 reference →

Related Ranges

Parent /20 block 100.97.208.0/20 Sibling /21 block 100.97.208.0/21

Adjacent Prefix Sizes

/19 8,190 hosts /20 4,094 hosts /21 2,046 hosts /22 1,022 hosts /23 510 hosts