3com iCV-01a User Manual

 
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. 
 

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 
 

0, 255 

Subnet masking 

127 

Loopback testing and interprocess communication on local devices 

224-254 

IGMP multicast and other special protocols.