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IP Line Description, Installation and Maintenance
902

Appendix E: Subnet Mask Conversion

from CIDR to Dotted Decimal Format

Introduction
Subnet masks are expressed in Classless InterDomain Routing (CIDR)
format, appended to the IP address, such as 10.1.1.1/20. The subnet mask
must be converted from CIDR format to dotted decimal format in order to
configure IP addresses.
The CIDR format expresses the subnet mask as the number of bits counting
from the most significant bit of the first IP address field. A complete IP
address consists of 32 bits. Therefore, a typical CIDR format subnet mask is
in the range from /9 to /30. Each decimal number field in the dotted decimal
format has a value from 0 to 255, where decimal 255 represents binary 1111
1111.
Follow the steps in Procedure 129 on page 902 to convert a subnet mask from
CIDR format to dotted decimal format.