Appendix D Subnet Mask Conversion From Cidr To Dotted Decimal Format; Introduction - Avaya Nortel Communication Server 1000 Manual

Appendix D
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
format to dotted decimal format" (page 545)
CIDR format to dotted decimal format.
Procedure 78
Converting a subnet mask from CIDR format to dotted decimal format
Step
1
2
Copyright © 2003–2008, Nortel Networks
.
Procedure 78 "Converting a subnet mask from CIDR
Action
Divide the CIDR format value by 8. The quotient (the number of
times that eight divides into the CIDR format value) equals the
number of dotted decimal fields containing 255.
In the example above, the subnet mask is expressed as /20. Twenty
divided by eight equals a quotient of two, with a remainder of four.
Therefore, the first two fields of the subnet mask in dotted decimal
format are 255.255.
If there is a remainder, see
(page 546) to obtain the dotted decimal value for the field following
the last field containing "255". In the example of /20 above, the
remainder is four. In
Nortel Communication Server 1000
IP Line Fundamentals
NN43100-500 02.02 Standard
Release 5.5 4 February 2008
to convert a subnet mask from
Table 156 "CIDR format remainders"
Table 156 "CIDR format remainders" (page
545