lextudio/sharpsnmplib

Idea to support Agents that only support 16-bit Request IDs

craigermcgreger opened this issue · 3 comments

craigermcgreger commented

Sharp SNMP has special support for broken Agents that don't support negative Request IDs via Messenger.UseFullRange = false, which restricts Request IDs to 0 thru int.MaxValue (2,147,483,647).

There is another type of broken Agent that only supports 16-bit Request IDs. In fact, they are so common that support for them was added to net-snmp almost 20 years ago:

  $ man snmp.conf

  16bitIDs yes
      restricts requestIDs, etc to 16-bit values.
      The SNMP specifications define these ID fields as
       32-bit quantities, and the Net-SNMP library typically
       initialises them to random values for security. However
       certain (broken) agents cannot handle ID values greater
       than 2^16 - this option allows interoperability with such agents.

Source

Currently, the only way to work with these agents in Sharp SNMP is to specify the Request ID manually by creating GetRequestMessage, SetRequestMessage, etc. It would be great if we could use Messenger with them, too. To do this, we could use a new enum, Messenger.RequestIDRange:

  • Full (default): int.MinValue thru int.MaxValue
  • Positive32Bit: 0 thru int.MaxValue
  • Positive16Bit: 0 thru short.MaxValue (32,767)

Messenger.UseFullRange could be obsoleted, but for backwards compatibility, setting Messenger.UseFullRange = true would set Messenger.RequestIDRange = Full and setting Messenger.UseFullRange = false would set Messenger.RequestIDRange = Positive32Bit.

lextm commented

It makes no sense to add more hacks in Messenger for specific agents (as we cannot assume how bad an agent can be). But it is possible to extract ID generation policies to their own classes so that anyone can customize further via a standardized API.

Might deliver it in the next release, as it shouldn't be a hard task.

lextm commented

You can try 12.5.0 Beta 6 and set Messenger.RequestCounter to control the ID range immediately when your program starts.

https://www.nuget.org/packages/Lextm.SharpSnmpLib/12.5.0-beta6

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craigermcgreger commented

I installed 12.5.0-beta6 and tried Messenger.RequestCounter = new NumberGenerator(0, short.MaxValue). It worked perfectly with the Agent that only accepts 16-bit Request IDs. Plus, it is much more flexible than my idea. Thank you!