Manager and agent relationship
As mentioned earlier, SNMP facilitates communication between a managed device (a
device with an SNMP agent—let’s say a router) and an SNMP manager or management
application. This basic relationship is illustrated in the Figure 5-5. Communication be‐
tween these two entities is achieved via the SNMP Protocol. These messages are typically
encapsulated in UDP packets, and four kinds of operations are permitted between
managers and agents (managed device). These operations are:
Get
The manager can perform a get (or read) to obtain information from the agent
about an attribute of a managed object.
Get-Next
The manager can perform a get-next to do the same for the next object in the tree
of objects on the managed device.
Get-Bulk
The manager can perform a get-bulk to obtain information about a group of data
from the agent. This is not possible in the case of SNMP V1.
Set
The manager can perform a set (or write) to set the value of an attribute of a
managed object.
In addition to these messages, an agent may emit a trap or a notification that represents
an asynchronous notification. These notifications are directed to one or more managers
and are intended to indicate that some event on the managed device has occurred.
In more modern, highly scaled systems, the CPU burden created by the work of the
SNMP agent (particularly when it interfaces with multiple managers) is often addressed
by creating a local hierarchy that includes distributed proxies. Tweaks to the agent op‐
eration itself (such as the number of records fetched in each access of tabular data) and
data management optimization techniques (such as local caching) are not uncommon.