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Appendix
This section discusses: Communities, Gateways, IP Addresses, and Sub net 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