TUT:snmpwalk

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The snmpwalk command is designed to perform a sequence of chained GETNEXT requests automatically, rather than having to issue the necessary snmpgetnext requests by hand.

Contents

Basic Example

The command takes a single OID, and will display a list of all the results which lie within the subtree rooted on this OID:

 % snmpwalk -v 2c -c demopublic test.net-snmp.org system
 SNMPv2-MIB::sysDescr.0 = HP-UX net-snmp B.10.20 A 9000/715
 SNMPv2-MIB::sysObjectID.0 = OID: enterprises.ucdavis.ucdSnmpAgent.hpux10
 SNMPv2-MIB::sysUpTime.0 = Timeticks: (586998396) 67 days, 22:33:03.96
 SNMPv2-MIB::sysContact.0 = Wes Hardaker wjhardaker@ucdavis.edu
 SNMPv2-MIB::sysName.0 = net-snmp
 SNMPv2-MIB::sysLocation.0 = UCDavis
 SNMPv2-MIB::sysORLastChange.0 = Timeticks: (0) 0:00:00.00
 SNMPv2-MIB::sysORID.1 = OID: SNMPv2-MIB::snmpMIB
 SNMPv2-MIB::sysORID.2 = OID: IF-MIB::ifMIB
 SNMPv2-MIB::sysORID.4 = OID: IP-MIB::ip
 SNMPv2-MIB::sysORID.5 = OID: UDP-MIB::udpMIB
 SNMPv2-MIB::sysORDescr.1 = The Mib module for SNMPv2 entities.
 SNMPv2-MIB::sysORDescr.2 = The MIB module to describe generic objects for network interface sub-layers
 SNMPv2-MIB::sysORDescr.4 = The MIB module for managing IP and ICMP implementations
 SNMPv2-MIB::sysORDescr.5 = The MIB module for managing UDP implementations
 SNMPv2-MIB::sysORUpTime.1 = Timeticks: (82) 0:00:00.82
 SNMPv2-MIB::sysORUpTime.2 = Timeticks: (81) 0:00:00.81
 SNMPv2-MIB::sysORUpTime.4 = Timeticks: (83) 0:00:00.83
 SNMPv2-MIB::sysORUpTime.5 = Timeticks: (82) 0:00:00.82

It can also be used with a single MIB (scalar) object, or even an exact instance OID - returning the corresponding value:

 % snmpwalk -v 2c -c demopublic test.net-snmp.org sysDescr
 SNMPv2-MIB::sysDescr.0 = HP-UX net-snmp B.10.20 A 9000/715
 % snmpwalk -v 2c -c demopublic test.net-snmp.org sysDescr.0 SNMPv2-MIB::sysDescr.0 = HP-UX net-snmp B.10.20 A 9000/715

Conversely, it's also possible to start the walk at a higher level, retrieving more than one group of information.

 % snmpwalk -v 2c -c demopublic test.net-snmp.org .iso

would typically retrieve all the information known to an agent. (Output omitted here, for obvious reasons!)


Walking tables

The first example above contains both scalar and table instances. Snmpwalk can also be used for retrieving a single column of a table, by specifying the column object as the starting point.

 % snmpwalk -v 2c -c demopublic test.net-snmp.org sysORID
 SNMPv2-MIB::sysORID.1 = OID: SNMPv2-MIB::snmpMIB
 SNMPv2-MIB::sysORID.2 = OID: IF-MIB::ifMIB
 SNMPv2-MIB::sysORID.4 = OID: IP-MIB::ip
 SNMPv2-MIB::sysORID.5 = OID: UDP-MIB::udpMIB

Note that when retrieving a full table (either alone, or as part of a wider walk), all the values for one column are displayed before moving on to the next. This can be seen in the output of walking the system group above.

This is precisely the behaviour described in the snmpgetnext tutorial for a chain of GETNEXT requests. However it sometimes comes as a surprise to those new to SNMP, who expect such tables to be displayed one row at a time. The snmptable command may provide a more familiar view of such tables.


Walking an empty tree

If the agent does not implement any MIB objects underneath the specified OID, then the snmpwalk command may return without displaying anything at all, or it may display a vaguely informative message, depending on the SNMP version being used:

 % snmpwalk -v 1 -c demopublic test.net-snmp.org ifXTable
 (nothing displayed)
 % snmpwalk -v 2c -c demopublic test.net-snmp.org ifXTable IF-MIB::ifXTable = No Such Object available on this agent at this OID

Alternatively, if the requested tree is later than the last MIB instance that the agent implements, a slightly different message will be displayed:

 % snmpwalk -v 1 -c demopublic test.net-snmp.org .2.0
 End of MIB
 % snmpwalk -v 2c -c demopublic test.net-snmp.org .2.0 joint-iso-ccitt.0 = No more variables left in this MIB View (It is past the end of the MIB tree)

But in each case, the meaning is the same - the agent had nothing relevant to display.

Exactly the same behaviour holds if the agent does implement MIB objects within the requested subtree, but the access control settings are configured to deny access to them. That is effectively the same as not implementing these objects at all. (At least for the given administrative information settings)


Multiple Values

The snmpwalk is designed to retrieve multiple OIDs and values from the remote agent. But unlike most of the other command-line tools, it can only work with a single starting OID. It is not possible to supply multiple OIDs as part of the same command.

Or more accurately - it is possible to specify several OIDs, but everything other than the first one will be ignored!



Tutorial Sections

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