I need a little bit of help to understand what Information the ipNetToPhysicalEntry OID 1.3.6.1.2.1.4.35.1 exactly includes. I thought its a combination between the Neighbor Cache and the ARP Cache, but when i read this OID over, lets say snmpwalk, i don´t get everything whats inside my Routers Neighbor Cache and ARP Cache. What are the criteria which information is inside and which not? And where can I see the definition for that ?
SNMP – Understanding ipNetToPhysicalEntry OID Transmission
ciscosnmp
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Best Answer
In addition to Ricky's answer, you can also use the
snmptranslate
utility to dump information about SNMP tables and how table entries are indexed, etc. The-Tp -IR
flags will tellsnmptranslate
to print a tree view of the table. A very useful (and overlooked) utility IMO.Here's the output for
ipNetToPhysicalTable
(which is the table object to which ipNetToPhysicalEntry belongs):Now you can see how an entry in the table is supposed to be indexed, and also the OIDs that make up the table. The first 3 entries are the indexes. Each entry in the table is going to have these 3 indexes - essentially ipNetToPhysicalIfIndex + ipNetToPhysicalNetAddressType + ipNetToPhysicalNetAddress. Then subsequently there are 5 "columns" in a row of this table:
Here's an example from one of my devices:
So think of this like a row entry in the table, and we've picked out column 1 from the row, which is ipNetToPhysicalPhysAddress. So in this particular entry, the
.1.ipv4."10.200.17.34"
part is the index of the entry. The 1 is the ifIndex of the interface that the ARP entry is learned on, 'ipv4' is the ipNetToPhysicalNetAddressType which is one of these:unknown(0), ipv4(1), ipv6(2), ipv4z(3), ipv6z(4), dns(16)
and finally, the IP address of the ARP entry, 10.200.17.34. These three things make up the index for that entry. Then the value for ipNetToPhysicalPhysAddress at that specific index is the MAC address748e.f862.5941
.This could very well be an issue with the SNMP implementation of your device (which you've given us zero information about by the way). It would be useful if you could edit your original question to include this information, as well as output from
snmpbulkwalk
against theipNetToPhysicalTable
table. Also, you could try doing ansnmpbulkwalk
againstipv6NetToMediaTable
to see if you get results from that.