ZyXEL Communications Prestige 320W Support Notes page 13

SNMP is a member of the TCP/IP protocol suite, it uses the UDP to exchange messages between a
management Client and an Agent, residing in a network node.
There are two versions of SNMP: Version 1 and Version 2. ZyXEL supports SNMPv1. Most of the
changes introduced in Version 2 increase SNMP's security capabilities. SNMP encompasses three main
areas:
1. A small set of management operations.
2. Definitions of management variables.
3. Data representation.
The operations allowed are: Get, GetNext, Set, and Trap. These functions operate on variables that exist
in network nodes. Examples of variables include statistic counters, node port status, and so on. All of the
SNMP management functions are carried out through these simple operations. No action operations are
available, but these can be simulated by the setting of flag variables. For example, to reset a node, a
counter variable named 'time to reset' could be set to a value, causing the node to reset after the time had
elapsed.
SNMP variables are defined using the OSI Abstract Syntax Notation One (ASN.1). ASN.1 specifies how
a variable is encoded in a transmitted data frame; it is very powerful because the encoded data is
self-defining. For example, the encoding of a text string includes an indication that the data unit is a string,
along with its length and value. ASN.1 is a flexible way of defining protocols, especially for network
management protocols where nodes may support different sets of manageable variables.
The net of variables that each node supports is called the Management Information Base (MIB). The
MIB is made up of several parts, including the Standard MIB, specified as part of SNMP, and Enterprise
Specific MIB, which are defined by different manufacturer for hardware specific management.
The current Internet-standard MIB, MIB-II, is defined in RFC 1213 and contains 171 objects. These
objects are grouped by protocol (including TCP, IP, UDP, SNMP, and other categories, including 'system'
and 'interface.'
The Internet Management Model is as shown in figure 1. Interactions between the NMS and managed
devices can be any of four different types of commands:
6. Reads
Read is used to monitor the managed devices, NMSs read variables that are maintained by the
devices.
All contents copyright (c) 2005 ZyXEL Communications Corporation.
P320W Support Notes
13