belloyang / snmp-subagent

See also http://www.net-snmp.org/wiki/index.php/TUT:Writing_a_Subagent

SNMP Subagent

Quick Start

$ make subagent-demon
$ sudo ./subagent-demon

SNMP Installation from source

$ git clone [e-mail]:net-snmp/net-snmp.git
$ cd net-snmp
$ ./configure
$ make
$ make install

Configure SNMPD

1. locate snmpd.conf under /etc/snmp/
2. Add the following lines to snmpd.conf:

• master agentx #enable Agentx master agent support
• rwcommunity public
• rocommunity public

3. restart snmp: sudo systemctl restart snmpd

SNMPD Extension

There are three approaches to extend snmpd function. This repository is using AgentX approach and is built separately. The other two approaches are: Approach 1:

1. write the MIB module (use mib2c to generate the template code, e.g. env MIBS="NANOMETRICS-MIB" mib2c mib2c.mfd.conf nmxCentaurScalars)
2. put the files generated in step 1 (nmxCentaurScalar.c/h) to net-snmp/agent/mibgroup/, and rebuild the net-snmp from the source:

• ./configure --with-mib-modules=nmxCentaurScalars
• make & make install

3. Restart snmpd which now includes the newly added MIB module implementation.

Approach 2:

1. use net-snmp-config:

• run net-snmp-config --compile-subagent mysubagent nmxCentaurScalars.c
• mysubagent executable willd be generated after successfully built.

2. run mysubagent as root. It will connect with the master agent snmpd and start supporting the new MIB module.

SNMP tools usages

1. send snmp get request for a MIB object

$ snmpget -c public localhost NANOMETRICS-MIB:nmxCentaurSohInteger.0

2. translate a MIB object to OID

$ snmptranslate -IR -On NANOMETRICS-MIB:nmxCentaurScalars

3. print the MIB tree structure starting from a MIB node

$ snmptranslate -IR -Tp NANOMETRICS-MIB:nmxCentaurScalars

Run snmp and subagent for debugging (non-root)

1. Start snmpd (as non-root) on customized ports

$ snmpd -f -Lo -C --rwcommunity=public --master=agentx --agentXSocket=tcp:localhost:1705 udp:1161

2. Connect the subagent (created by approach 2) to the customized tcp port.

$ ./mysubagent -f -Lo -x tcp:localhost:1705

3. Run snmp tool on the udp port to quiry MIB object

$ snmpget -c public localhost:1161 NANOMETRICS-MIB:nmxCentaurSohInteger.0

Issues and Solutions

1. libnetsnmpmibs.so.* not found while executing the subagent

• verify that libnetsnmpmibs.so.* is located under /usr/local/lib/
• Add the path to LD_LIBRARY_PATH and run the subagent: export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib
• While running the subagent as root, the LD_LIBRARY_PATH doesn't work. /usr/local/lib needs to be added to /etc/ld.so.conf and then run sudo ldconfig.

2. Check if the custom mib module has been built into libnetsnmpmibs.so

• nm /usr/local/lib/libnetsnmpmibs.so.40