TCP/IP Tutorial and Technical Overview - IBM Redbooks

SNMP
Manager
walk ifType
ifMtu.1=d
ifType.1 = a
ifType.2 = b
ifType.3 = c
walk returned
ifType.1=a
ifType.2=b
ifType.3=c
Note that, had the getNext request been for an object in the System Group or
SNMP Group MIBs, the SNMP agent would have recognized the object and
responded directly to the manager. No subagent would have been involved in
this circumstance.
While the concept of the get, getNext, getBulk, and set processes are
somewhat simple, the process of executing a walk warrants additional
discussion. As noted previously, a walk request is never actually sent to the
SNMP agent. Instead, the walk is a manager convention, and is implemented as
a series of getNext requests. In each iteration of the series, the object returned
previously by the agent becomes the next object specified on the getNext
request. The first time the agent returns a value outside of the range specified on
the walk request, the walk ends. To demonstrate this, assume that there are
three instances of ifType at the time a walk is issued for the ifType object: ifType.1
through ifType.3. The processing of the walk proceeds as illustrated in
Figure 17-6.
getNext ifType
ifType.1 = a
getNext ifType.1
Figure 17-6 An example of a walk on ifType
SNMP
Agent
getNext ifType
ifType.1 = a
getNext ifType.1
ifType.2 = b ifType.2 = b
getNext ifType.2
getNext ifType.2
ifType.3 = c ifType.3 = c
getNext ifType.3
ifMtu.1-d
getNext ifType.3
ifMtu.1-d
TCPIP
Sub-agent
Interface MIB
ifDescr.2
ifDescr.3
ifType
ifType.1 = a
ifType.2 = b
ifType.3 = c
ifMtu
ifMtu.1=d
ifMtu.2=e
ifMtu.3=f
ifSpeed
ifSpeed.1=g
ifSpeed.2=h
ifSpeed.3=i
ifPhysAddress
Chapter 17. Network management 637