Minuteman UPS SNMP-32 Series - Manual (Page 36)

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9. Appendix
This section discusses: Communities, Gateways, IP Addresses, and Subnet masking.
Communities
A community is a string of printable ASCII characters that identifies a user group with the same access privileges. For
example, a common community name is “public.”
For security purposes, the SNMP agent validates requests before responding. The agent can be configured so that only
trap managers that are members of a community can send requests and receive responses from a particular community.
This prevents unauthorized managers from viewing or changing the configuration of a device.
Gateways
Gateway, also referred to as a router, is any computer with two or more network adapters connecting to different physical
networks. Gateways allow for transmission of IP packets among networks on an Internet.
IP Addresses
Every device on an Internet must be assigned a unique IP (Internet Protocol) address. An IP address is a 32-bit value
comprised of a network ID and a host ID. The network ID identifies the logical network to which a particular device
belongs. The host ID identifies the particular device within the logical network. IP addresses distinguish devices on an
Internet from one another so that IP packets are properly transmitted.
IP addresses appear in dotted decimal (rather than in binary) notation. Dotted decimal notation divides the 32-bit value
into four 8-bit groups, or octets, and separates each octet with a period. For example, 199.217.132.1 is an IP address in
dotted decimal notation.
To accommodate networks of different sizes, the IP address has three divisions—Classes A for large, B for medium, and
C for small. The difference among the network classes is the number of octets reserved for the network ID and the
number of octets reserved for the host ID.
Class Value of First Octet Network ID Host ID Number of Hosts
A 1-126 First octet Last three octets 16,387,064
B 128-191 First two octets Last two octets 64,516
C 192-223 First three octets Last octet 254
Any value between 0 and 255 is valid as a host ID octet except for those values the InterNIC reserves for other purposes.
Value Purpose
0, 255 Subnet masking
127 Loopback testing and interprocess communication on local devices
224-254 IGMP multicast and other special protocols
Subnetting and Subnet Masks
Subnetting divides a network address into sub-network addresses to accommodate more than one physical network on a
logical network.
For example: A Class B company has 100 LANs (Local Area Networks) with 100 to 200 nodes on each LAN. To classify
the nodes by its LANs on one main network, this company segments the network address into 100 sub-network
addresses. If the Class B network address is 150.1.x.x, the address can be segmented further from 150.1.1.x through
150.1.100.x.