Unit installation

Appendix B SNMP Management Installation and Operation Manual
B-4 IP Environment FCD-E1
Access Restriction Using SNMP Communities
In general, SNMP agents support two types of access rights:
• Read-only − the SNMP agent accepts and processes only SNMP getRequest
and getNextRequest commands from management stations which have a
read-only community name.
• Read-write − the SNMP agent accepts and processes all the SNMP commands
received from a management station with a read-write community name.
SNMP agents are usually configured to send traps to management stations
having read-write communities.
In accordance with the SNMP protocol, the SNMP community of the originating
entity is sent in each message.
When an SNMP message is received by the addressed entity, first it checks the
originator's community: messages with community names not included in the
SNMP community names table of the recipient are discarded (SNMP agents of
managed entities usually report this event by means of an authentication failure
trap).
The SNMP agents of managed entities evaluate messages originated by
communities appearing in the agent's SNMP community names table in
accordance with the access rights, as explained above. Thus a setRequest for a
MIB object with read-write access rights will nevertheless be rejected if it comes
from a management station whose community has read-only rights with respect to
that particular agent.
B.3 IP Environment
This section provides general information on the IP environment.
IP Address Structure
Under the IP protocol, each IP network element (SNMP agents, network
management stations, etc.) is called an IP host and must be assigned an IP address.
An IP address is a 32-bit number, usually represented as four 8-bit bytes. Each byte
represents a decimal number in the range of 0 through 255.
The address is given in decimal format, with the bytes separated by decimal points,
e.g., 164.90.70.47. This format is called dotted quad notation.
An IP address is logically divided into two main portions:
• Network Portion − The network portion is assigned by the Internet Assigned
Numbers Authority (IANA). There are five IP address classes: A, B, C, D, and E.
However, only the classes A, B and C are used for IP addressing. Consult your
network manager with respect to the class of IP addresses used on your
network.