Appendix B: IP Address, Subnet and Gateway
Appendix B: IP Address, Subnet and Gateway
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
Network lD
Host lD
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 tree 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.
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