TUT:Using TLS
Note: Features discussed on this page require Net-SNMP version 5.6 or higher.
"SNMP over DTLS over UDP" and "SNMP over TLS over TCP" (RFC5953) are supported in Net-SNMP 5.6 and beyond. This page describes how to use DTLS or TLS for the end user. For information on the administering and configuring the agent with DTLS/TLS support, see Using_DTLS.
TLS and DTLS make use of the Transport Security Model (TSM) security model, defined in RFC5591 which was created as an alternative to the USM security model (which is discussed in the SNMPv3 Options tutorial.
Contents
DTLS vs TLS
TLS and DTLS are both protocols that protect packets in transit. The first runs over TCP porto 10161 and the second over UDP port 10161, which both have unique advantages (and a discussion of those advantages is beyond scope of this tutorial).
Below you'll find examples that use both the dtlsudp: prefix and the tlstcp: prefix. Our test.net-snmp.org server will respond to both transports so you can try them both out.
Required Build Options
You must have added these options when configure was run to make the following tutorial work:
--with-security-modules=tsm --with-transports="DTLSUDP TLSTCP"
Zero-config Example
Importing the tutorial certificates
You must download and install the certificates you will use to connect to the agent (tutorial-joecool), the certificate that the agent will present for verification (tutorial-agent) and the certificate authority that signed the agent's certificate (tutorial-CA). The net-snmp-cert utility can import the certificate and put them in the proper locations for you.
$ net-snmp-cert -t tutorial-joecool import \
http://www.net-snmp.org/tutorial/tutorial-5/certificates/tutorial-joecool.crt \
http://www.net-snmp.org/tutorial/tutorial-5/certificates/tutorial-joecool.key
$ net-snmp-cert -t tutorial-agent import \
http://www.net-snmp.org/tutorial/tutorial-5/certificates/tutorial-agent.crt
$ net-snmp-cert -t tutorial-CA import \
http://www.net-snmp.org/tutorial/tutorial-5/certificates/tutorial-CA.crt
Querying the Net-SNMP test server
In these examples, test.net-snmp.org is the host name of the agent to query, using version 3 of the SNMP protocol and the transport security model, and an authPriv message protected a dtls connection using the certificates identified by the given certificate tags. The OID being requested is sysUpTime.0 from the MIB module SNMPv2-MIB.
First we directly specify both our identity and the identity we expect the agent to present:
$ snmpget -T our_identity=tutorial-joecool \
-T their_identity=tutorial-agent \
-t 10 tls:test.net-snmp.org sysUpTime.0
You can also specify a trusted certificate authority (CA) for the agent, instead of a specific certificate:
$ snmpget -T our_identity=tutorial-joecool \
-T trust_cert=tutorial-CA \
-t 10 tls:test.net-snmp.org sysUpTime.0
Once you add certificate options to your configuration files, you no longer need to specify certificate on the command line:
$ echo trustCert tutorial-CA >> $HOME/.snmp/snmp.conf $ echo clientCert tutorial-joecool >> $HOME/.snmp/snmp.conf $ snmpget -t 10 tls:test.net-snmp.org sysUpTime.0
Obtaining and using test.net-snmp.org certificates
You will need the certificates for the Net-SNMP test server and test user for this tutorial. A compressed tarball is avaialable here, along with its gpg signature. Or you can download the individual files as well:
The net-snmp-cert command is able to pull these certificates directly from a URL, as shown in the previous example.
Extracting the tarball
If you retrieved the entire certificate tar-ball, extract it as follows:
Once you have the tutorial-.snmp tarball, uncompress it in your home directory:
$ tar xvfz tutorial-.snmp.tar.gz .snmp/ .snmp/snmp.conf.tutorial .snmp/tls/ .snmp/tls/newcerts/ .snmp/tls/private/ .snmp/tls/private/tutorial-joecool.key .snmp/tls/ca-certs/ .snmp/tls/ca-certs/tutorial-CA.crt .snmp/tls/certs/ .snmp/tls/certs/tutorial-joecool.crt .snmp/tls/certs/tutorial-agent.crt
You can use net-snmp-cert to show you the certificates (and their fingerprints):
$ net-snmp-cert showcert /home/dummy/.snmp/tls: certs/tutorial-agent.crt: subject= /C=US/ST=California/O=Net-SNMP Developers/OU=SNMP-TLS/CN=tutorial-agent/emailAddress=tutorial-agent@test.net-snmp.org certs/tutorial-joecool.crt: subject= /C=US/ST=California/O=Net-SNMP Developers/OU=SNMP-TLS/CN=Joe Cool/emailAddress=joe.cool@test.net-snmp.org
$ net-snmp-cert showcert --fingerprint /home/dummy/.snmp/tls: certs/tutorial-agent.crt: SHA1 Fingerprint=CA:B8:0A:B3:6B:4C:21:2A:F2:92:CD:0B:6B:DF:6A:9F:23:D6:30:4B certs/tutorial-joecool.crt: SHA1 Fingerprint=CD:74:45:C9:A3:A3:55:0A:6C:37:03:B2:49:38:B1:01:99:95:8E:43
Querying the demo agent
Querying using filenames for keys
Now that you have the certificates, you can query the test agent using the file names:
snmpget -T our_identity=tutorial-joecool \
-T their_identity=tutorial-agent \
tlstcp:test.net-snmp.org sysContact.0
Querying using fingerprints for keys
or the fingerprints:
snmpget -T our_identity=CD:74:45:C9:A3:A3:55:0A:6C:37:03:B2:49:38:B1:01:99:95:8E:43 \
-T their_identity=CA:B8:0A:B3:6B:4C:21:2A:F2:92:CD:0B:6B:DF:6A:9F:23:D6:30:4B \
tls:test.net-snmp.org sysContact.0
Querying using a trusted CA certificate and their properly encoded hostname
You can also specify that you trust the host CA and expect the remote certificate to have it's host name in its certificate file that matches your command line:
snmpget -T our_identity=tutorial-joecool \
-T trustCert=tutorial-CA \
tlstcp:test.net-snmp.org sysContact.0
(this won't work if their presented certificate doesn't contain "test.net-snmp.org")
Setting up configuration
Those are long ugly command lines, so you might want to add some defaults in your configuration file, snmp.conf. There is an included snmp.conf file, but to ensure that we don't overwrite any existing snmp.conf it must be appended to your existing configuration file.
$ cat $HOME/.snmp/snmp.conf.tutorial >> $HOME/.snmp/snmp.conf
Now try this much simpler query:
$ snmpget tls:test.net-snmp.org sysContact.0 SNMPv2-MIB::sysContact.0 = STRING: Net-SNMP Coders <net-snmp-coders@lists.sourceforge.net>
Getting tutorial certificates into a Java Keystore
If you need to use a Java client for testing, you have to jump through a few hoops to get Java to use the tutorial certificates.
Public Certificates
Importing certificates is pretty easy.
keytool -import -keystore net-snmp.jks -alias tutorial-ca -file ca-certs/tutorial-CA.crt
Keytool doesn't like the text expansion of the certificate, so copy the agent certificate and delete everything before '-----BEGIN CERTIFICATE-----'.
cp certs/tutorial-agent.crt /tmp/tutorial-agent.crt vi /tmp/tutorial-agent.crt keytool -import -keystore net-snmp.jks -alias tutorial-agent -file /tmp/tutorial-agent.crt
Private Keys
Private keys, not so easy.
First convert them to DER:
openssl x509 -in certs/tutorial-joecool.crt -inform PEM -out joecool-cert.der -outform DER openssl pkcs8 -topk8 -nocrypt -in private/tutorial-joecool.key -inform PEM -out joecool-key.der -outform DER
Java's keytool can't import private keys, so we have to rely on the kindness of strangers. In this case, Neal Groothuis. Head over to http://www.nealgroothuis.name/import-a-private-key-into-a-java-keystore/ and cut-and-paste his KeyStoreImport.java code to a local file. WARNING: KeyStoreImport will echo your password!
javac KeyStoreImport.java java KeyStoreImport net-snmp.jks joecool-cert.der joecool-key.der joecool
Check your work:
keytool -list -keystore net-snmp.jks
Tutorial Sections
About the SNMP Protocol
These tutorial links talk about SNMP generically and how the protocol itself works. They are good introductory reading material and the concepts are important to understand before diving into the later tutorials about Net-SNMP itself.
- How SNMP Works: About the protocol itself (GETs, GETNEXTs, etc)
- What data is in SNMP: All about SNMP Management Information Bases (MIBs)
- Securing SNMP: How to use the SNMP protocol securely
Net-SNMP Command Line Applications
These tutorial pages discuss the command line tools provided in the Net-SNMP suite of tools. Nearly all the example commands in these tutorials works if you try it yourself, as they're all examples that talk to our online Net-SNMP test agent. Given them a shot!
- snmptranslate: learning about the MIB tree.
- snmpget: retrieving data from a host.
- snmpgetnext: retrieving unknown indexed data.
- snmpwalk: retrieving lots of data at once!
- snmptable: displaying a table.
- snmpset: peforming write operations.
- snmpbulkget: communicates with a network entity using SNMP GETBULK request
- snmpbulkwalk: retrieve a sub-tree of management values using SNMP GETBULK requests.
- snmptrap: Sending and receiving traps, and acting upon them.
- Traps/informs with SNMPv3/USM: Sending and receiving SNMPv3/USM TRAPs and INFORMs
- Sending Traps/Informs via AgentX: Sending notifications from the command line through snmpd
- Common command line options:
- Using and loading MIBS
- SNMPv3/USM Options
- Using SNMPv3 over TLS and DTLS
- Customized Output Formats
- Writing mib2c config files
Application Configuration
All of our applications support configuration to allow you to customize how they behave.
Net-SNMP Daemons
Net-SNMP comes with two long-running daemons: a SNMP agent (snmpd) for responding to management requests and a notification receiver (snmptrapd) for receiving SNMP notifications.
- SNMP Agent (snmpd) Configuration
- SNMP Notification Receiver (snmptrapd)
- Agent Monitoring
Coding Tutorials
Net-SNMP comes with a highly flexible and extensible API. The API allows you to create your own commands, add extensions to the agent to support your own MIBs and perform specialized processing of notifications.
- Client / Manager Coding Tutorials
- Agent Coding Tutorials
- The Agent Architecture page might be worth reading before or after the agent coding tutorials, and describes how the Agent Helpers work under the hood.
- Writing a mib module to serve information described by an SNMP MIB, and how to compile it into the net-snmp snmpd agent.
- Writing a Dynamically Loadable Object that can be loaded into the SNMP agent.
- Writing a Subagent that can be run to attach to the snmpd master agent.
- Writing a perl plugin to extend the agent using the NetSNMP::agent module.
- Writing shell scripts to extend the agent
- Using mib2c to help write an agent code template for you
- Header files and autoconf
Debugging SNMP Applications and Agents
All our tools and applications have extensive debugging output. These tutorials talk about how the debugging system works and how you can add your own debugging statements to you code:
- Debugging output printed using the -D command line option
- Using -Ddump to display packet breakdowns
- Debugging using GDB
Operating System Specific Tutorials
- Building With Visual Studio 2005 Express
- Building Net-SNMP 64-bit with Visual C++ 2010 Express
- Net-Snmp on Ubuntu
- Net-SNMP and lm-sensors on Ubuntu 10.04
- Net-SNMP for windows:
