/21 Subnet
A /21 has 2,048 addresses, 2,046 of them usable by hosts. Its netmask is 255.255.248.0. Enter any address below to see its /21 network.
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Examples:
IPv4 network
2,046 usable hosts · 192.168.0.1 to 192.168.7.254
Details
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/21 at a glance
A /21 fixes the first 21 bits of the address as the network and leaves 11 bits for hosts, so it holds 2^11 = 2,048 addresses. The first is the network address and the last is the broadcast address, leaving 2,046 for hosts.
A /21 is 8 /24 networks side by side; registries and ISPs allocate blocks this size to networks that route them on the internet.
A /21 can be announced in BGP on its own: /24 is the longest prefix most networks accept.
Questions
How many usable IP addresses are in a /21?
What is the subnet mask for /21?
How many /24 networks are in a /21?
Is 255.255.248.0 the same as /21?
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