Do SNMP Informs Guarantee No Data Loss?

snmp

I am working on a monitoring application, using SharpSNMPLib on C#. I was using SNMP Traps but found out that there are some traps that are lost. Now I am using SNMP Informs.

Do you think that this counters the loss (because Informs are acknowledged traps), or is it pretty much the same thing?

Best Answer

It really depends on the sender. For instance, if it is a fatal event, it is unlikely that the sender will be able to resend an unacknowledged event. In general, informs are more reliable than traps, but there is no guarantee that a sender will resend an unacknowledged inform, only that the sender can resend an unacknowledged inform.

This is how Cisco explains informs, SNMP Inform Request:

SNMP Inform Request

The SNMP Inform Request feature supports sending inform requests. SNMP asynchronous notifications are usually sent as SNMP traps.

Traps are less reliable than informs because an acknowledgment is not sent from the receiving end when a trap is received; however, an SNMP manager that receives an inform acknowledges the message with an SNMP response PDU. If the sender does not receive a response for an inform, the inform can be sent again.

Related Solutions

SNMP ENGINE process has high CPU usage on a few 6500 chassis

I would take a look at this support document from Cisco.

In part it recommends to run the following command to see which OID's were recently polled:

show snmp stats oid

This gives a readout for which OID's you are polling. It will allow you to see, by judging the time stamps, which OID is taking a long time to poll. This is usually where your problem lies. See the below sample output:

asr1001-1#show snmp stats oid

time-stamp               #of times requested             OID
20:31:33 EDT May 25 2013         1142                    ifOutDiscards
20:31:33 EDT May 25 2013         1142                    ifOutErrors
20:31:33 EDT May 25 2013         1142                    ifInDiscards
20:31:33 EDT May 25 2013         1142                    ifInErrors
20:31:33 EDT May 25 2013         1142                    ifHCOutOctets
20:31:33 EDT May 25 2013         1902                    ifHCInOctets

However do note that it was only added in IOS release 12.4(20)T and 12.0(22)S, so may not be available to you.

In the linked document there are some other methods such as:

Sniffing the packets on the port to see what OID's are being polled heavily
Using debug snmp packets

They aren't as nice and neat as the show snmp stats oid but they can help you out if that command isn't available.

Cisco – How to view not-accessible SNMP indexes? MPLS implementation

It may happen that the OID`s you are querying are not implemented on the device. It may happen that either those are not supported or not implemented.

Just in case for your verification you can use "-Cc" option of snmpwalk which will give you the whole MIB.

Best Answer

Related Solutions

SNMP ENGINE process has high CPU usage on a few 6500 chassis

Cisco – How to view not-accessible SNMP indexes? MPLS implementation

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