Ethernet Connection, cont’d
A-6 ISM 824 Integrated Scaling Multiswitcher • Reference Information
Subnetting — A Primer
It is not the purpose of this manual to describe TCP/IP protocol in detail. However,
some understanding of TCP/IP subnetting (a subnet is a subset of a network — a
set of IP devices that have portions of their IP addresses in common) is necessary in
order to understand the interaction of the ISM 824 and the mail server gateway. To
understand subnetting at the level required to install and operate the ISM 824, you
must understand the concepts of a gateway, local and remote devices, IP addresses
and octets, and subnet masks and octets.
Gateways
The ISM 824 can communicate with the e-mail server that the switcher uses for
e-mail notification directly (if they are on the same subnet) or the communication
can be routed via a gateway (a computer that provides a link between different
subnets).
Local and remote devices
The local and remote devices are defined from the point of view of the function
being described. In this manual, subnetting is an issue when you are using the
controlling PC to set TCP/IP and e-mail values in the ISM 824 (see “IP Settings
window” in chapter 5, “Switcher Software”, and “System Settings page”, in
chapter 6, “HTML Operation”). When you are setting up the variables for e-mail
notification, which may include subnetting, the seamless switcher is the local
device and the e-mail server is the remote device.
IP addresses and octets
Valid IP addresses consist of four 1-, 2-, or 3-digit numeric subfields, properly called
octets, separated by dots (periods) (figure A-4). Each octet can be numbered from
000 through 255. Leading zeroes, up to 3 digits total per octet, are optional. Values
of 256 and above are invalid.
192.168.254.254Typical IP Address:
Octets
Figure A-4 — IP address and octets
Subnet masks and octets
The subnet mask (figure A-5) is used to determine whether the local and remote
devices are on the same subnet or different subnets. The subnet mask consists
of four numeric octets separated by dots. Each octet can be numbered from
000 through 255. Leading zeroes, up to 3 digits total per octet, are optional. Each
octet typically contains either 255 or 0. The octets determine whether or not the
same octets of two IP addresses will be compared when determining if two devices
are on the same subnet.
255.255.0.0Typical Subnet Mask:
Octets
255 indicates that this octet will be
compared between two IP addresses.
0 indicates that this octet will not be
compared between two IP addresses.
Figure A-5 — Subnet mask and octets