NetFlow Lab/Protocol Labs/SNMP
Simulated
Mission

Watch a router: measure how busy port Gi0/2 is, then catch the alarm when it fails.

Start here

What is SNMP?

SNMP — Simple Network Management Protocol — is how a monitoring server keeps an eye on routers, switches and servers. It asks them questions such as “how much traffic?” on UDP port 161, and they can raise an alarm of their own on port 162.

  1. 1Pick a story

    Start with “Watch a router”. “Keep it private” shows the secure version.

  2. 2Press Next

    One message at a time travels between the two machines.

  3. 3Read what happened

    Switch to Technical or Packet whenever you want more detail.

  4. 4Try it for real

    Every step shows the command that sends the same message.

ready
7 steps
Monitoring server10.0.0.50asks the questions
Nothing sent yet — press Next
Router10.0.0.1answers, and raises alarms
Gi0/0Gi0/1Gi0/2
What happened

A monitoring server wants to keep an eye on a router. Press Next to send its first question.

The server knows the router’s address and one shared password, “public”. With SNMPv2c that is all it needs — and anyone else who sees that password can ask too.

Think first · step 1 of 7

The server wants to know how long the router has been up. What kind of message does it send?

See the real packetfields and values appear once a message is sent

nms 10.0.0.50 · agent 10.0.0.1:161 · community public · poll interval 60 s

Practise on your own computer5 steps · Ubuntu, or Windows with WSL

Practise only on your own computer, or on devices you have permission to test. The agent set up here listens on 127.0.0.1, so nothing outside your computer can reach it.

  1. 1
    Open a Linux terminal

    On Windows, open PowerShell as administrator, run this, restart, then open “Ubuntu” from the Start menu. Already on Ubuntu? Skip this step.

    wsl --install
  2. 2
    Install the tools, the agent and the trap receiver

    snmp gives you snmpget and the other commands, snmpd is the agent that answers them, and snmptrapd receives alarms.

    sudo apt update
    sudo apt install -y snmp snmpd snmptrapd
  3. 3
    Let the agent share its interface counters

    Out of the box the agent answers only on 127.0.0.1 and shares only basic system information. This one line adds the interface table.

    echo 'view systemonly included .1.3.6.1.2.1.2' | sudo tee -a /etc/snmp/snmpd.conf
    sudo service snmpd restart
  4. 4
    Create the SNMPv3 user nms-ro

    The agent has to be stopped while its user file is edited, and each password needs at least 8 characters.

    sudo service snmpd stop
    echo 'createUser nms-ro SHA-256 "authpass123" AES "privpass123"' | sudo tee -a /var/lib/snmp/snmpd.conf
    echo 'rouser nms-ro priv' | sudo tee -a /etc/snmp/snmpd.conf
    sudo service snmpd start
  5. 5
    Allow the lab’s traps

    The trap receiver drops every alarm until it is told which community to accept. Stopping the background copy frees port 162 for the one you start by hand.

    echo 'authCommunity log public' | sudo tee -a /etc/snmp/snmptrapd.conf
    sudo service snmptrapd stop

Done — now pick any step above and run its command.