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Chapter 9
TCP/IP – network terms
Exigo tool manual
Chapter 9
TCP/IP – network terms
9.1 Networks, subnets, routers
IP network
An
IP network
is a cluster of cables and devices, where an equipment with one IP address can
communicate with any other IP addressed equipment. Internet is
one
network, and when your home
computer connects to the Internet, you become part of the Internet.
Subnet
Networks are divided into
subnets
, which are linked with
routers
. Routers need some kind of map of
the network (or at least of the closest subnets, and somewhere to send everything else). A computer
only needs to know the address of the closest router. A local switched Ethernet network is
one
subnet.
Routers can have several Ethernet ports for different Ethernet networks, or maybe an Ethernet port
and an ADSL connection.
9.2 IP address, Subnet mask, Default Gateway, DNS server
IP address
Each computer or network connected controller has an IP address consisting of four numbers between
0 and 255, making up a total of 32 bits.
Subnet mask
Each computer or network connected controller also has a subnet mask consisting of 32 bits.
Example
If the IP address is 192.0.2.73 and the subnet mask is 255.255.255.0, then the subnet addresses are
from 192.0.2.0 up to 192.0.2.255, and 192.0.2.73 is your address on the subnet. Sometimes the subnet
mask is specified by the number of bits used (always starting at the beginning of the subnet mask).
The subnet is then 192.0.2.0/24, and the IP address and the subnet mask can also be specified together:
192.02.73/24.
Default Gateway
Each computer and each controller using TCP/IP communication must know the IP address to the
router that goes out from its subnet. The IP address of this router is usually called the
default gateway
.
All traffic that shall be sent out of your own subnet is sent to the default gateway.
DNS name
The computer or the controller must know the address of the equipment it is going to communicate
with. This can be given as an IP address or a
DNS name
. DNS is a name service which can translate
hierarchical names like
exomaincomputer.regincontrols.com
to an IP address. Several
DNS servers are part of the system, but you only have to know the IP address to one of them.