72
CTI Janus Programmable Automation Controller IOG
This can be accomplished by using the Windows calculator Programmer view. Using this example, you would enter
the value of the third octet (40), click
on the “and” button, enter the S
ubnet M
ask (240), and then click on the “=”
button. The result, in this case, is 32. Thus, the Network Address is 127.18.32.0.
CIDR Notation
CIDR notation (Classless Inter-Domain Routing) is an alternate method of representing a subnet mask. It is simply a
count of the number of network bits (bits that are set to 1) in the subnet mask. It provides a more concise way to
represent the subnet mask.
The CIDR number is typically preceded by a slash “/” and follows the IP address. For
example, an IP address of 131.10.55.70 with a subnet mask of 255.0.0.0 (which has 8 network bits) would be
represented as 131.10.55.70 /8. The following table can be used to convert between subnet mask and CIDR.
CIDR
Dotted Decimal
CIDR
Dotted Decimal
/1
128.0.0.0
/17
255.255.128.0
/2
192.0.0.0
/18
255.255.192.0
/3
224.0.0.0
/19
255.255.224.0
/4
240.0.0.0
/20
255.255.240.0
/5
248.0.0.0
/21
255.255.248.0
/6
252.0.0.0
/22
255.255.252.0
/7
254.0.0.0
/23
255.255.254.0
/8
255.0.0.0
/24
255.255.255.0
/9
255.128.0.0
/25
255.255.255.128
/10
255.192.0.0
/26
255.255.255.192
/11
255.224.0.0
/27
255.255.255.224
/12
255.240.0.0
/28
255.255.255.240
/13
255.248.0.0
/29
255.255.255.248
/14
255.252.0.0
/30
255.255.255.252
/15
255.254.0.0
/31
255.255.255.254
/16
255.255.0.0
/32
255.255.255.255
Selecting an IP Address
The Janus Controller typically requires a fixed IP Address. If you are connecting to an existing network, you should
obtain an unused static IP Address and Subnet Mask from the network administrator.
If you are establishing your own IP Addresses, you should select IP Addresses from a block of
‘private” addresses
established by the Internet Assigned Numbers Authority (IANA). The private address blocks are:
•
10.0.0.0 through 10.255.255.255 (Class A)
•
172.16.0.0 through 172.31.255.255 (Class B)
•
192.168.0.0 through 192.168.255.255 (Class C)
These addresses will not be forwarded by the Internet backbone routers; therefore, you are free to use any
address in this group as long as it does not conflict with the usage by your local organization.
