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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.

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RAD Data comm FCD-X21 Manual de instalación Pagina 154