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https://github.com/guycole/snmp-lab

Experiments extending the Net-SNMP agent
https://github.com/guycole/snmp-lab

c net-snmp net-snmp-extension snmp snmp-agent snmpd

Last synced: 11 days ago
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Experiments extending the Net-SNMP agent

Host: GitHub
URL: https://github.com/guycole/snmp-lab
Owner: guycole
Created: 2024-12-06T00:59:04.000Z (17 days ago)
Default Branch: main
Last Pushed: 2024-12-08T23:10:18.000Z (14 days ago)
Last Synced: 2024-12-09T00:20:56.380Z (14 days ago)
Topics: c, net-snmp, net-snmp-extension, snmp, snmp-agent, snmpd
Homepage:
Size: 24.4 KB
Stars: 0
Watchers: 1
Forks: 0
Open Issues: 1
Metadata Files:
- Readme: README.md

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README

# snmp-lab
Experiments extending the Net-SNMP agent

## Introduction
This project is to share my experience in extending the [Net-SNMP](https://en.wikipedia.org/wiki/Net-SNMP) agent by creating a custom [MIB](https://en.wikipedia.org/wiki/Management_information_base) and then populating the generated stubs from mib2c(1).

I am writing this in November, 2024 and the current source version of Net-SNMP is 5.9.4, my development box is a ThinkPad on Ubuntu 22 LTS (Jammy Jellyfish).

## Building Net-SNMP from scratch
1. Obtain and unpack the source tar ball.
1. ./configure (there will be interactive questions)
1. I use SNMPv2c for development and use SNMPv3 for production.
1. My configuration summary:

```
---------------------------------------------------------
Net-SNMP configuration summary:
---------------------------------------------------------

SNMP Versions Supported: 1 2c 3
Building for: linux
Net-SNMP Version: 5.9.4.pre2
Network transport support: Callback Unix Alias TCP UDP TCPIPv6 UDPIPv6 IPv4Base SocketBase TCPBase UDPIPv4Base UDPBase IPBase IPv6Base
SNMPv3 Security Modules: usm
Agent MIB code: default_modules => snmpv3mibs mibII ucd_snmp notification notification-log-mib target agent_mibs agentx disman/event disman/schedule utilities host
MYSQL Trap Logging: unavailable
Embedded Perl support: enabled
SNMP Perl modules: building -- embeddable
SNMP Python modules: disabled
Crypto support from: use_pkg_config_for_openssl
Authentication support: MD5
Encryption support:
Local DNSSEC validation: disabled

---------------------------------------------------------
```

1. make;sudo make install
1. binaries installed in /usr/local/bin and /usr/local/sbin
1. headers installed in /usr/local/include/net-snmp
1. libraries installed in /usr/local/lib
1. mib installed in /usr/local/share/snmp/mibs

1. configuration files for snmp utilities and snmpd
1. configuration files reside in /usr/local/share/snmp
1. examples:
[snmp.conf (utilities)](https://github.com/guycole/snmp-lab/blob/main/config/snmp.conf)
[snmpd.conf (snmpd)](https://github.com/guycole/snmp-lab/blob/main/config/snmpd.conf)
1. copy these or use snmpconf(1) to generate your own

1. almost there!
1. snmpd(8) does not install as a systemd service
1. logs to /var/log/snmpd.log

## Test run vanilla agent
1. (optional) I like to run tcpdump(8) to see the agent traps.
1. Ensure snmpd.conf has the correct IP address for your "manager" (i.e. development machine)
1. ```tcpdump -v port 162```

1. Run snmpd
1. Must run as root for port 161
1. I prefer to run snmpd(8) in the foreground while developing
1. Start the agent like ```./snmpd -f -V```
1. Should have observed the start trap (via tcpdump)

1. Tail the log
1. ```tail -f /var/log/snmpd.log```
1. Should a version message waiting for you

1. Exercise the agent
1. ```snmpwalk -v 2c -c public localhost system```
1. You should see something like this:
```
gsc@waifu:138>snmpwalk -v 2c -c public localhost system
MODULE-IDENTITY MACRO (lines 55..79 parsed and ignored).
OBJECT-IDENTITY MACRO (lines 81..103 parsed and ignored).
OBJECT-TYPE MACRO (lines 212..298 parsed and ignored).
NOTIFICATION-TYPE MACRO (lines 302..334 parsed and ignored).
TEXTUAL-CONVENTION MACRO (lines 8..48 parsed and ignored).
SNMPv2-MIB::sysDescr.0 = STRING: Linux waifu 6.8.0-49-generic #49~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Wed Nov 6 17:42:15 UTC 2 x86_64
SNMPv2-MIB::sysObjectID.0 = OID: NET-SNMP-MIB::netSnmpAgentOIDs.10
DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (14624) 0:02:26.24
SNMPv2-MIB::sysContact.0 = STRING: mongohax
SNMPv2-MIB::sysName.0 = STRING: waifu
SNMPv2-MIB::sysLocation.0 = STRING: margaritaville
SNMPv2-MIB::sysServices.0 = INTEGER: 12
SNMPv2-MIB::sysORLastChange.0 = Timeticks: (0) 0:00:00.00
SNMPv2-MIB::sysORID.1 = OID: SNMP-FRAMEWORK-MIB::snmpFrameworkMIBCompliance
SNMPv2-MIB::sysORID.2 = OID: SNMP-MPD-MIB::snmpMPDCompliance
SNMPv2-MIB::sysORID.3 = OID: SNMP-USER-BASED-SM-MIB::usmMIBCompliance
SNMPv2-MIB::sysORID.4 = OID: SNMPv2-MIB::snmpMIB
SNMPv2-MIB::sysORID.5 = OID: SNMP-VIEW-BASED-ACM-MIB::vacmBasicGroup
SNMPv2-MIB::sysORID.6 = OID: TCP-MIB::tcpMIB
SNMPv2-MIB::sysORID.7 = OID: UDP-MIB::udpMIB
SNMPv2-MIB::sysORID.8 = OID: IP-MIB::ip
SNMPv2-MIB::sysORID.9 = OID: SNMP-NOTIFICATION-MIB::snmpNotifyFullCompliance
SNMPv2-MIB::sysORID.10 = OID: NOTIFICATION-LOG-MIB::notificationLogMIB
SNMPv2-MIB::sysORDescr.1 = STRING: The SNMP Management Architecture MIB.
SNMPv2-MIB::sysORDescr.2 = STRING: The MIB for Message Processing and Dispatching.
SNMPv2-MIB::sysORDescr.3 = STRING: The management information definitions for the SNMP User-based Security Model.
SNMPv2-MIB::sysORDescr.4 = STRING: The MIB module for SNMPv2 entities
SNMPv2-MIB::sysORDescr.5 = STRING: View-based Access Control Model for SNMP.
SNMPv2-MIB::sysORDescr.6 = STRING: The MIB module for managing TCP implementations
SNMPv2-MIB::sysORDescr.7 = STRING: The MIB module for managing UDP implementations
SNMPv2-MIB::sysORDescr.8 = STRING: The MIB module for managing IP and ICMP implementations
SNMPv2-MIB::sysORDescr.9 = STRING: The MIB modules for managing SNMP Notification, plus filtering.
SNMPv2-MIB::sysORDescr.10 = STRING: The MIB module for logging SNMP Notifications.
SNMPv2-MIB::sysORUpTime.1 = Timeticks: (0) 0:00:00.00
SNMPv2-MIB::sysORUpTime.2 = Timeticks: (0) 0:00:00.00
SNMPv2-MIB::sysORUpTime.3 = Timeticks: (0) 0:00:00.00
SNMPv2-MIB::sysORUpTime.4 = Timeticks: (0) 0:00:00.00
SNMPv2-MIB::sysORUpTime.5 = Timeticks: (0) 0:00:00.00
SNMPv2-MIB::sysORUpTime.6 = Timeticks: (0) 0:00:00.00
SNMPv2-MIB::sysORUpTime.7 = Timeticks: (0) 0:00:00.00
SNMPv2-MIB::sysORUpTime.8 = Timeticks: (0) 0:00:00.00
SNMPv2-MIB::sysORUpTime.9 = Timeticks: (0) 0:00:00.00
SNMPv2-MIB::sysORUpTime.10 = Timeticks: (0) 0:00:00.00
```

1. If all this works out, congratulations you have built a working snmpd (agent).

## Extend the agent to support a custom MIB
1. In this section, I use a simple custom MIB to generate C stubs via [mib2c(1)](https://net-snmp.sourceforge.io/tutorial/tutorial-5/toolkit/mib2c/index.html) and then add these to snmpd, followed by verification via snmpwalk(1).

## Demo MIB
1. Start off simple with two scalars in [GUY-COLE-SCALAR-MIB](https://giithub.com/guycole/snmp-lab/blob/main/mib/GUY-COLE-SCALAR-MIB.txt).
1. Copy GUY-COLE-SCALAR-MIB.txt to /usr/local/share/snmp/mibs
1. Seed your environment: ```export MIBS="+GUY-COLE-SIMPLE-MIB"```
1. Validate: ```snmptranslate -IR guyColeSimple``` (should run without error).
1. Run mib2c(1): ```mib2c guyCole```
1. The OID 1.3.6.1.4.1.5088 is based on my IANA enterprise assignment.
1. Pick "Net-SNMP style code"
1. Pick "writing code for generic some scalars"
1. Generates two files: "guyCole.h" and guyCole.c"
1. Configure and build snmpd(8) for new MIB
1. Copy the generated files to the Net-SNMP directory, i.e. "net-snmp-5.9.4/agent/mibgroup"
1. Run configure again: ```./configure --with-mib-modules="guyCole"```
1. My configuration summary:
```
---------------------------------------------------------
Net-SNMP configuration summary:
---------------------------------------------------------

SNMP Versions Supported: 1 2c 3
Building for: linux
Net-SNMP Version: 5.9.4.pre2
Network transport support: Callback Unix Alias TCP UDP TCPIPv6 UDPIPv6 IPv4Base SocketBase TCPBase UDPIPv4Base UDPBase IPBase IPv6Base
SNMPv3 Security Modules: usm
Agent MIB code: default_modules guyCole => snmpv3mibs mibII ucd_snmp notification notification-log-mib target agent_mibs agentx disman/event disman/schedule utilities host
MYSQL Trap Logging: unavailable
Embedded Perl support: enabled
SNMP Perl modules: building -- embeddable
SNMP Python modules: disabled
Crypto support from: use_pkg_config_for_openssl
Authentication support: MD5
Encryption support:
Local DNSSEC validation: disabled

---------------------------------------------------------
```
1. make;sudo make install
1. Exercise the agent
1. Restart the agent with logging enabled
1. ```./snmpd -DguyCole -f -V```
1. Invoke snmpwalk(1)
```
gsc@waifu:355>snmpwalk -v 2c -c public localhost 1.3.6.1.4.1.5088.1.1
SNMPv2-SMI::enterprises.5088.1.1.0 = INTEGER: 0
```
1. Set fresh integer value using snmpset(1)
```
snmpset -v 2c -c private localhost 1.3.6.1.4.1.5088.1.1.0 i 5
SNMPv2-SMI::enterprises.5088.1.1.0 = INTEGER: 5
```
1. Verify update
```
snmpwalk -v 2c -c public localhost 1.3.6.1.4.1.5088.1.1
SNMPv2-SMI::enterprises.5088.1.1.0 = INTEGER: 5
```

476 snmpset -v 2c -c private localhost 1.3.6.1.4.1.5088.1.2.0 s "aaaaa"
477 snmpwalk -v 2c -c public localhost 1.3.6.1.4.1.5088.1

[Net-SNMP Coding Documentation](https://net-snmp.sourceforge.io/dev/agent/index.html)
http://www.net-snmp.org/wiki/index.php/Agent_Architecture
https://openhpi.sourceforge.net/subagent-manual/index.html