Actually the snmplibrary already has a way of binding the ports. In my $HOME/.snmp/snmp.conf I just add this:
[asyncapp] #doDebugging 1 clientaddr 10.0.0.1:12345 clientaddrUsesPort yes asyncapp is the name of my program. I have bound outbound connections with a source port of 12345 on interface 127.0.0.1 (for testing) 10.0.0.1 is the local IP address of the computer that's sending the request. Wireshark shows this: User Datagram Protocol, Src Port: 12345, Dst Port: 161 On Thu, 7 Jan 2021 at 15:03, Ed Fair <quacksp...@gmail.com> wrote: > Craig, > > The tutorials don't mention subsessions or traditional vs single session > use, but the header/c files do (and that's all they do - mention them). > I'm just curious what these abstractions are for since they seem, on the > surface, related to my needs. > > As an exercise, I've tried but so far been unable to create a > session/socket which uses a specific port - no errors, but no pdus/packets > transmitted. And anyway, I don't care if the port selected is random, my > goal is to use *the same* port to query multiple agents. I don't care how > it's done, as long as the end result is "all outbound UDP use same SRC > port". > > > On Wed, Jan 6, 2021, 5:28 AM Craig Small <csm...@dropbear.xyz> wrote: > >> On Wed, 6 Jan 2021 at 10:01, Ed Fair <quacksp...@gmail.com> wrote: >> >>> Thanks for the reply. The Simple_Async_Application in your link uses >>> one session/socket/SRC port per agent. I've compiled and run this sample >>> successfully, but I haven't been able to modify it to use a single >>> session/socket/SRC port. >>> >> It might need to be something more low-level as reusing sockets >> (therefore the ports) is generally a bad idea. >> >> The netsnmp_session has an attribute of local_port. If this is set to >> zero (the default) then it picks it randomly. I'd try setting that and see >> what happens. A quick look in the snmplib source code shows it is used for >> creating the transport. >> >> I understand "don't hammer agents" but I don't understand your "one query >>> per agent" limit - is this a limitation of the API? >>> >> Not at all, a lot of agents are terrible and do stupid things like have >> exclusive locks on important components of the system. I've killed many >> devices (the remote agents, not my code) by being too enthusiastic about >> querying them. >> >> >>> I'm new to this API, I might be missing key concepts... but I am >>> confused by the "traditional vs single" distinction, and I'm curious what >>> "subsessions" are. >>> >> Are either of those mentioned in the tutorial? They could mean multiple >> things but was trying to find the context of what you are asking here. >> >> - Craig >> >
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