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SPF CIDR Calculator

Work out an IP range and the exact ip4:/ip6: SPF mechanism.

[ About this tool ]

This SPF CIDR calculator works out the network, netmask, first and last address and address count for any IPv4 or IPv6 range, and gives you the exact ip4: or ip6: mechanism.

How to read the results

›Use the network address, not a host inside the range.
›Wide ranges such as /8 let others send as you.
›Only authorise IP ranges you control.

Frequently asked questions

What does /24 mean in SPF?

ip4:203.0.113.0/24 authorises all 256 addresses from 203.0.113.0 to 203.0.113.255.

Learn more in our guide: SPF (Sender Policy Framework)

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