SNMPWALK is one of the main tools used by a network engineer to troubleshoot behavior or verify configuration of devices. The output however is pretty hard to understand. In this article, we will talk about how Unbrowse SNMP makes the task of working with SNMPWALK dumps much easier. Snmpwalk is a command line utility available on almost all router platforms. A standalone version is also available for free from the excellent Net-SNMP project.

You may also want to check out this 5-min screencast !

Lexicographic ordering in SNMP

What does the SNMPWALK command do ?

The SNMPWALK command is used to retrieve a MIB subtree and print the results to the console. In reality, there is no "WALK" operation defined in the SNMP protocol. The SNMPWALK actually tool uses a series of GETNEXT requests in a loop. The first iteration of GETNEXT uses the OID supplied on the command line, all  subsequent GETNEXTs use the OID contained in the previous response. The loop stops if the returned OID in the response is outside the subtree of the original OID or the end of MIB is reached.

Sample outputs

$snmpwalk -v 1 -c public123 localhost .1.3.6.1
sysDescr.0 = STRING: Software: Whistler Version 5.1 Service Pack 2 (Build 2600)
sysObjectID.0 = OID: win32
sysUpTimeInstance = Timeticks: (15535) 0:02:35.35
sysContact.0 = STRING: unknown
sysName.0 = STRING: UDLDEV
sysLocation.0 = STRING: unknown
sysServices.0 = INTEGER: 72
sysORID.4 = OID: snmpMPDCompliance 

The problem with the output

A lot of network administrators have to deal with raw snmpwalk outputs such as the ones shown above. This causes a lot of aggravation for the following reasons.

• Hard to visualize especially for MIB tables, because we are trying to visualize a two dimensional table using a one dimensional dump of text output.
• If the snmpwalk output contains OIDs instead of names, then we are completely lost.
• We cannot easily navigate to the definition of each node or look at the textual convention or type of the value.
• A graphical table is better than plain text !

Example :  Walk the HOST-RESOURCE mib disk partition table

This is the raw output from the snmpwalk command

.1.3.6.1.2.1.25.3.7.1.1.1537.1 = INTEGER: 1
.1.3.6.1.2.1.25.3.7.1.1.1537.2 = INTEGER: 2
.1.3.6.1.2.1.25.3.7.1.1.1537.3 = INTEGER: 3
.1.3.6.1.2.1.25.3.7.1.2.1537.1 = STRING: "/dev/hdb1"
.1.3.6.1.2.1.25.3.7.1.2.1537.2 = STRING: "/dev/hdb2"
.1.3.6.1.2.1.25.3.7.1.2.1537.3 = STRING: "/dev/hdb3"
.1.3.6.1.2.1.25.3.7.1.3.1537.1 = STRING: "0x341"
.1.3.6.1.2.1.25.3.7.1.3.1537.2 = STRING: "0x342"
.1.3.6.1.2.1.25.3.7.1.3.1537.3 = STRING: "0x343"
.1.3.6.1.2.1.25.3.7.1.4.1537.1 = INTEGER: 14877060 KBytes
.1.3.6.1.2.1.25.3.7.1.4.1537.2 = INTEGER: 9920624 KBytes
.1.3.6.1.2.1.25.3.7.1.4.1537.3 = INTEGER: 0 KBytes
.1.3.6.1.2.1.25.3.7.1.5.1537.1 = INTEGER: 1
.1.3.6.1.2.1.25.3.7.1.5.1537.2 = INTEGER: 3
.1.3.6.1.2.1.25.3.7.1.5.1537.3 = INTEGER: 0

The above text when run through the import feature in Unbrowse SNMP produces a spreadsheet-like walker as shown below.

Go to the Unbrowse SNMP Page

How to convert an SNMPWALK output into a nice spreadsheet like table ?

Unbrowse SNMP makes it dramatically easier to work with output of snmpwalk commands. You send in a text file containing the snmpwalk output, and you will get a MyMib (which corresponds to the subtree extracted by the snmpwalk command) and a Spreadsheet like view of the results. This helps you boost your productivity because you no longer have to scratch your head when confronted with a large snmpwalk dump.

You can use this feature by importing a file or by "copy-paste"

Via a file import

If you have a file containing the snmpwalk output, you can select the “File > Import > From SNMPWALK dump” command. The exact steps are outlined below.

• Close all browser and walker windows
• Select File->Import->From a SNMPWALK dump.. menu item
• Select the snmpwalk dump file
• A status window appears indicating progress, you can stop at any time.
• Unresolved OIDs are MIB objects in the snmpwalk dump that are not known to Unbrowse SNMP. These unresolved OIDs are shown in the text area on the status window.
• During SNMPWALK processing:
• First a MyMIB is created containing all the objects in the snmpwalk input file. You can save it for use later.
• Next the MIB Walker view (a spreadsheet like view) is created
• Please be patient as this may take time if the input file is large. It can take upto 2 minutes to fully construct the sheet when large inputs are selected.
• You can save the MyMIB and the Walker view, or export the Walker view to HTML for easier offline analysis

Via the clipboard ( copy-paste method)

If you have the snmpwalk dump in an email, a website, or a bug report, you can just copy paste the text into a special window. To use this feature, select “File > Import > From a SNMPWALK dump in the clipboard”. Paste the text into the box and press “Import!”

Supported snmpwalk formats

Unbrowse SNMP allows you to enter the snmpwalk output in a variety of formats. These may even be intermingled in the same input file. Most popular formats of Cisco, Juniper, and Net-SNMP are supported.