Craig - You are exactly right - the config file allows me to control this - thank you so much! I couldn't use the [application name] syntax, but simply adding these two lines to the end of the config file had the desired effect of causing all outbound SNMP from SRC PORT 30000:
clientaddr :30000 clientaddrUsesPort yes I'll work to understand how to use the [program name] approach next. I'm guessing the init_snmp() call sets the program name used. ed On Sun, Jan 10, 2021 at 6:48 PM Craig Small <csm...@dropbear.xyz> wrote: > 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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