IPRangeExplorer

121.6.40.0/21

Public

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

Network Address
121.6.40.0
Broadcast Address
121.6.47.255
Subnet Mask
255.255.248.0
Usable Hosts
2,046
First Usable IP
121.6.40.1
Last Usable IP
121.6.47.254
Total IPs
2,048
Prefix Length
/21

Network address — the base address of the block (121.6.40.0). All devices in this subnet share this prefix. Cannot be assigned to a host.

Broadcast address — packets sent to 121.6.47.255 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 121.6.40.0/21
Network Address 121.6.40.0
Broadcast Address 121.6.47.255
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 121.6.40.1
Last Usable IP 121.6.47.254
Network (Hex) 0x79062800
Broadcast (Hex) 0x79062FFF
Address Type Public / Globally Routable

Binary Representation

Network Address
01111001.00000110 01111001.00000110.00101000.00000000
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 121.6.40.0/21 into 2 equal /22 subnets (1,022 usable hosts each).

# CIDR Network First Usable Last Usable Broadcast Hosts
1 121.6.40.0/22 121.6.40.0 121.6.40.1 121.6.43.254 121.6.43.255 1,022
2 121.6.44.0/22 121.6.44.0 121.6.44.1 121.6.47.254 121.6.47.255 1,022

/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 121.6.32.0/20 Sibling /21 block 121.6.32.0/21

Adjacent Prefix Sizes

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

Calculate Another