Festo SBO***-Q Series, Руководство пользователя

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A. Technical appendix
A-5
Festo P.BE-SBO-Q-EN en 1602e
Net mask Which of the numbers in an IP address represent the net ID
and which the host ID is defined through specification of a
so-called “net mask”.
The telephone number of Festo Germany can be used as an
example to explain IP addresses and net masks:
00497113470
To know which part of this number is the dialling code and
which the subscriber number, it is additionally necessary to
know: “that the first 7 digits are the dialling code, and the last
4 the subscriber number”. This is the “net mask” of the tele­
phone number.
Net classes Using “0” as a placeholder, the net mask for IP addresses
defines which bytes are used for the addressing of the slave
(host ID). Networks belong to different net classes according
to the number of such bytes:
Net class Net mask Explanation
A 255.0.0.0 Large network
B 255.255.0.0 Medium-sized network
C 255.255.255.0 Small network with max.
254slaves
Tab. A/1: The main network classes with their correspond­
ing net masks (example)
Gateway Networks with different network IDs are connected to each
other via routers or gateways. If a slave in a network is to
send data to slaves in other networks, the IP address of the
gateway must be specified.