255.255.248.0 Subnet Mask
255.255.248.0 is the subnet mask for a /21 network — 2,046 usable hosts out of 2,048 addresses.
CIDR Prefix
/21
Wildcard Mask
0.0.7.255
Total Addresses
2,048
Usable Hosts
2,046
Network Bits
21
Host Bits
11
255.255.248.0 in Binary
Each octet is eight bits. The highlighted bits are the 21 network bits; the rest are the 11 host bits that vary within the subnet.
255
255
248
0
Networks Using 255.255.248.0
| Network | Host Range | Broadcast |
|---|---|---|
| 10.0.0.0/21 | 10.0.0.1 – 10.0.7.254 | 10.0.7.255 |
| 172.16.0.0/21 | 172.16.0.1 – 172.16.7.254 | 172.16.7.255 |
| 192.168.0.0/21 | 192.168.0.1 – 192.168.7.254 | 192.168.7.255 |
Neighbouring Masks
Frequently Asked Questions
What CIDR prefix is 255.255.248.0?
255.255.248.0 is /21 in CIDR notation. The mask sets the first 21 of the 32 bits in an IPv4 address to 1, marking them as the network portion, and leaves the remaining 11 bits as 0 for hosts.
How many hosts does 255.255.248.0 allow?
A network with mask 255.255.248.0 holds 2,048 addresses, of which 2,046 are usable by hosts — the network address and the broadcast address are reserved.
What is the wildcard mask for 255.255.248.0?
The wildcard mask for 255.255.248.0 is 0.0.7.255. It is the bitwise inverse: every 1 in the subnet mask becomes a 0 and every 0 becomes a 1. Cisco access lists and OSPF network statements take the wildcard form rather than the subnet mask.
Standards
- RFC 950 — Internet Standard Subnetting Procedure
Defines the dotted-decimal subnet mask itself, and the rule that the network and broadcast addresses are not assignable to hosts.
- RFC 4632 — Classless Inter-Domain Routing (CIDR)
Establishes the /21 prefix notation that 255.255.248.0 is equivalent to, and requires masks to be contiguous — which is why exactly 33 of the 4.3 billion possible values are valid.