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Home > Success Center > User Device Tracker (UDT) > UDT - Knowledgebase Articles > SNMP Context polling in UDT

SNMP Context polling in UDT

Updated March 11th, 2016


This article discusses how UDT conducts context-based polling against routers and switches for VLAN-based endpoints at a layer 2 level, and IP-based information from ARP entries on a configured VRF at a layer 3 level.


UDT 2 and later


Standard UDT-based polling gathers information for both MAC and IP endpoints through SNMP polling of Bridge MIB based OIDs.


However, standard OID polling for that information is not applicable to endpoints on a VLAN or a VRF. For this, UDT uses a context SNMP request against a device to gather information specifically for those VLANs and VRFs. This method allows for it to gather information specific only to a particular VLAN or VRF from a device that a standard poll will not grab.



For SNMPv2, this is conducted by adding the context at the end of the community string.

For example, when attempting to query a device using a community string of public against the OID of 1.3.6, it will return standard information for all the OIDs in that directory. However, if you add the VLAN or VRF to the end of the community string (public@103, for example), the walk or application is specifically asking just for information on those OIDs relevant to that VLAN or VRF. 


How to run an SNMPwalk.




SNMPv3 works similarly to SNMPv2 but not through a community. The following shows the actual context method available in the walk:



See SNMPv3 Bridge-MIB commands need to be added to Cisco devices for information on setting up context polling in SNMPv3.


With context polling, UDT  attempts to poll for all VLAN and VRF data for the endpoint information located on ports attached to a VLAN. This context polling is conducted on five OIDs: three specific to Layer 2, and two specific to Layer 3.

  • dot1dBasePortTable@VLAN =
  • dot1dTpFdbTable@VLAN =
  • dot1qTpFdbTable@VLAN =


  • ipNetToMediaTable@VRF =
  • ipNetToPhysicalTable@VRF =


Using the UDT Compatibility Checker tool, you can see the results of this context polling:


In some cases, gathering VLAN information is not possible. Refer to the following articles for similar scenarios:


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