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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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getBulkRequest Performs the same function as the get request, but allows<br />

the manager to query more than one object per request.<br />

This is only valid using the SNMPv2c security model (see<br />

“The GetBulkRequest” on page 642).<br />

setRequest Requests that the SNMP agent set the value of the<br />

specified object.<br />

walk Implements a series of getNext requests such that an<br />

entire sequence of objects is returned to the manager. In<br />

each iteration of the getNext series, the last object<br />

returned becomes the next object on which a getNext is<br />

executed. The walk ends when an object is returned that<br />

is beyond the scope of the request. An example of this is<br />

provided in Figure 17-6 on page 637.<br />

17.1.4 The SNMP subagent<br />

632 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong><br />

Note that the walk request is not architected in the SNMP<br />

communication that occurs between the SNMP manager<br />

<strong>and</strong> SNMP agent. Instead, it is a convention widely used<br />

by most SNMP managers.<br />

An SNMP subagent supports its own MIB, which might be an RFC-architected<br />

MIB, or might be a proprietary (referred to as enterprise-specific) MIB. For<br />

example, a <strong>TCP</strong>/<strong>IP</strong> subagent would most likely support the <strong>IP</strong>, ICMP, <strong>TCP</strong>, UDP,<br />

<strong>and</strong> Interface groups defined in RFC 1213. However, an individual software<br />

company might want use SNMP to make available information specific to their<br />

software. To do this, they can create a subagent that supports their<br />

enterprise-specific MIB.<br />

The subagent, upon initializing, opens a DPI connection to the SNMP agent. This<br />

occurs by first querying the agent, as though the subagent were a manager, for<br />

information about the agent’s DPI ports. Note that this information is maintained<br />

by the SNMP agent in the following two objects:<br />

dpiPortFor<strong>TCP</strong>.0 1.3.6.1.4.1.2.2.1.1.1.0<br />

dpiPortForUDP.0 1.3.6.1.4.1.2.2.1.1.2.0<br />

The agent’s response directs the subagent to the correct port over which a DPI<br />

connection can be opened. With this information, the subagent can interact with<br />

the agent, as described in 11.2.3, “The SNMP distributed programming interface<br />

(SNMP DPI)” on page 419.

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