TUT:snmpwalk
From Net-SNMP Wiki
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.
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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
- Command Line Applications
- snmptranslate: learning about the MIB tree.
- snmpget: retrieving data from a host.
- snmpgetnext: retrieving unknown indexed data.
- snmpwalk: retrieving lots of data at once!
- snmptable: displaying a table.
- snmpset: peforming write operations.
- snmpbulkget: communicates with a network entity using SNMP GETBULK request
- snmpbulkwalk: retrieve a sub-tree of management values using SNMP GETBULK requests.
- snmptrap: Sending and receiving traps, and acting upon them.
- Traps/informs with SNMPv3: Sending and receiving SNMPv3 TRAPs and INFORMs
- Common command line options:
- Writing mib2c config files
- SNMP Daemons
- SNMP Agent (snmpd) Configuration
- SNMP Notification Receiver (snmptrapd)
- Agent Monitoring
- Coding Tutorials
- Client / Manager Coding Tutorials
- Agent Coding Tutorials
- Writing a mib module to serve information described by an SNMP MIB, and how to compile it into the net-snmp snmpd agent.
- Writing a Dynamically Loadable Object that can be loaded into the SNMP agent.
- Writing a Subagent that can be run to attach to the snmpd master agent.
- Writing a perl plugin to extend the agent using the NetSNMP::agent module.
- Using mib2c to help write an agent code template for you
- Header files and autoconf
- Building With Visual Studio 2005 Express
- Debugging SNMP Applications and Agents
