Nortel Networks NN43001-563 Appendix D Subnet mask conversion from CIDR to dotted decimal format

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Appendix D
Subnet mask conversion from CIDR to
dotted decimal format
Subnet masks can be expressed in Classless Inter Domain Routing (CIDR)
format, appended to the IP address (for example, 10.1.1.1/20). The subnet
mask must be converted from CIDR format to dotted decimal format to
configure ITG IP addresses.
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. A typical CIDR format subnet mask is in the
range from /9 to /30. Each decimal number field in the dotted decimal format
can have a valuefrom 0 to 255, where 255 represents binary 1111 1111.
Follow the steps in Procedure 76 "Converting a subnet mask from CIDR
format to dotted decimal format" (page 457) to convert a subnet mask from
CIDR format to dotted decimal format.
Procedure 76
Converting a subnet mask from CIDR format to dotted decimal format
Step Action
1Divide the CIDR format valueby 8. The result is equal to the number
of dotted decimal fields containing 255.
In the example above, (10.1.1.1/20), the subnet mask is /20. 20
divided by 8 is equal to 2, with a remainder of 4. The first 2 fields of
the subnet mask in dotted decimal format are 255.255.
2If there is a remainder, referto Table 87 "CIDR format remainders"
(page 458) to get the dotted decimal value for the field followingthe
last field containing "255".
Nortel Communication Server 1000
IP TrunkFundamentals
NN43001-563 02.01 Standard
Release 5.5 21 December 2007
Copyright© 2007, Nor tel Networks
.