Install Zeek on Debian 11


Follow through this tutorial to learn how to install Zeek on Debian 11. Zeek, formerly Bro IDS, is the world’s leading passive open source network security monitoring tool. Zeek is not an active security device, like a firewall or intrusion prevention system. Rather, Zeek sits on a “sensor”, a hardware, software, virtual, or cloud platform that quietly and unobtrusively observes network traffic. Zeek interprets what it sees and creates compact, high-fidelity transaction logs, file content, and fully customized output, suitable for manual review on disk or in a more analyst-friendly tool like a security and information event management (SIEM) system.

Install Zeek on Debian 11

Zeek can be installed by building it from the source code or by directly via the Zeek APT repositories.

In this tutorial, we will install Zeek via the APT repositories.

Install Zeek on Debian 11

To install Zeek on Debian 11 from the Zeek APT repositories;

  • Add Zeek repository to Debian 11:
apt update && apt install curl gnupg2 -y
echo 'deb /' > /etc/apt/sources.list.d/zeek.list
curl -fsSL | gpg --dearmor > /etc/apt/trusted.gpg.d/security_zeek.gpg
  • Install Zeek on Debian 11

Next, run system update;

apt update

Zeek 4.1.1 is the current stable release as of this writing, confirm the same by running the command below;

apt-cache policy zeek
  Installed: (none)
  Candidate: 4.1.1-0
  Version table:
     4.1.1-0 500
        500  Packages

You can then install Zeek by running the command below;

apt install zeek -y

During the installation, you maybe prompted for some Postfix settings and if so, choose Internet Site and enter your system FQDN.

Configuring Zeek on Debian 11

Configure the Run-Time Environment

By default, Zeek is installed under /opt/zeek.

To begin the configuration with, add Zeek binaries path to PATH;

echo "export PATH=$PATH:/opt/zeek/bin" > /etc/profile.d/
source /etc/profile.d/

Define the Local Networks

Next, you need to tell Zeek which networks should be considered local to the monitored environment. This can be specified in the /opt/zeek/etc/networks.cfg configuration file.

The default networks defined are,,

cat /opt/zeek/etc/networks.cfg
# List of local networks in CIDR notation, optionally followed by a
# descriptive tag.
# For example, "" or "fe80::/64" are valid prefixes.          Private IP space       Private IP space      Private IP space

So, in our case, is our local network.


vim /opt/zeek/etc/networks.cfg
# List of local networks in CIDR notation, optionally followed by a
# descriptive tag.
# For example, "" or "fe80::/64" are valid prefixes.

#          Private IP space
#       Private IP space
#      Private IP space      Kifarunix-demo IP space

Save the file and exit once you made your network configuration changes.

Define Zeek Running Mode

Zeek can be run in standalone mode or in a clustered setup. It runs in standalone mode by default.

To define whether to run in a clustered or standalone setup, you need to edit the /opt/zeek/etc/node.cfg configuration file.

  • For a standalone configuration, there must be only one Zeek node defined in this file.
  • For a cluster configuration, at a minimum there must be a manager node, a proxy node, and one or more worker nodes.

According to Zeek quickstart guide, using the standalone / single process mode of Zeek is not suitable for setups with significant amounts of traffic. In these cases one will almost certainly want to make use of a Zeek cluster, even on a single system.

Therefore, we will see how to setup Zeek cluster. You can have a look at Zeek cluster architecture.

The default Zeek node configuration is like;

cat /opt/zeek/etc/node.cfg
# Example ZeekControl node configuration.
# This example has a standalone node ready to go except for possibly changing
# the sniffing interface.

# This is a complete standalone configuration.  Most likely you will
# only need to change the interface.

## Below is an example clustered configuration. If you use this,
## remove the [zeek] node above.


Since we are running a single node Zeek Cluster in this setup, comment out the Zeek standalone configuration, section under [zeek] and define host address for your Zeek logger, manager, proxy and worker.

So what are these components;

  • logger: it is an optional Zeek process that receives log messages from the rest of the nodes in the cluster. It can be used instead of the manager to reduce the load on the manager itself.
  • manager: receives log messages and notices from the rest of the nodes in the Zeek cluster if no logger is defined.
  • proxy: is a Zeek process that may be used to offload data storage or any arbitrary workload. A cluster may contain multiple proxy nodes.
  • worker: is the Zeek process that sniffs network traffic and does protocol analysis on the reassembled traffic streams.

So below is our single node Zeek cluster configuration setup;

cat /opt/zeek/etc/node.cfg
# Example ZeekControl node configuration.
# This example has a standalone node ready to go except for possibly changing
# the sniffing interface.

# This is a complete standalone configuration.  Most likely you will
# only need to change the interface.

## Below is an example clustered configuration. If you use this,
## remove the [zeek] node above.


Review Global ZeekControl configuration file

Next, you need to review the global ZeekControl configuration file, /opt/zeek/etc/zeekctl.cfg.

Most of the default values in configuration files should suffice. The only change you might want to make or update here is the recipient address for all emails sent out by Zeek and ZeekControl, if you have any set. The default value is root@localhost.

Validate Zeek Configuration

Before you can install and start Zeek, you need to validate the configuration file;

zeekctl check
Hint: Run the zeekctl "deploy" command to get started.
kifarunix-demo-zeek-logger scripts are ok.
kifarunix-demo-zeek-manager scripts are ok.
kifarunix-demo-zeek-proxy scripts are ok.
kifarunix-demo-zeek-worker scripts are ok.
kifarunix-demo-worker-lo scripts are ok.

Installing Zeek configurations

If there are no issues with the configuration, then you can install the configuration by running the command below;

zeekctl install

Running Zeek

Once you have installed the Zeek configuration, you can start it using the command;

zeekctl start

You can combine the install and start commands using the deploy command. i.e, instead of running zeekctl install and then zeekctl start, you can combine the two using the command;

zeekctl deploy

Check the status of Zeek Instance

You can check the status of Zeek instance by executing;

zeekctl status
Name         Type    Host             Status    Pid    Started
kifarunix-demo-zeek-logger logger    running   17911  17 May 03:52:41
kifarunix-demo-zeek-manager manager    running   17962  17 May 03:52:43
kifarunix-demo-zeek-proxy proxy    running   18011  17 May 03:52:45
kifarunix-demo-zeek-worker worker    running   18081  17 May 03:52:48
kifarunix-demo-worker-lo worker  localhost        running   18082  17 May 03:52:48

Other ZeekControl commands

Other zeek control/management commands are described on the zeekctl help page;

zeekctl help

ZeekControl Version 2.3.0-5

  capstats [] []      - Report interface statistics with capstats
  check []                  - Check configuration before installing it
  cleanup [--all] []        - Delete working dirs (flush state) on nodes
  config                           - Print zeekctl configuration
  cron [--no-watch]                - Perform jobs intended to run from cron
  cron enable|disable|?            - Enable/disable "cron" jobs
  deploy                           - Check, install, and restart
  df []                     - Print nodes' current disk usage
  diag []                   - Output diagnostics for nodes
  exec                  - Execute shell command on all hosts
  exit                             - Exit shell
  install                          - Update zeekctl installation/configuration
  netstats []               - Print nodes' current packet counters
  nodes                            - Print node configuration
  peerstatus []             - Print status of nodes' remote connections
  print  []             - Print values of script variable at nodes
  process  [] [-- ] - Run Zeek with options and scripts on trace
  quit                             - Exit shell
  restart [--clean] []      - Stop and then restart processing
  scripts [-c] []           - List the Zeek scripts the nodes will load
  start []                  - Start processing
  status []                 - Summarize node status
  stop []                   - Stop processing
  top []                    - Show Zeek processes ala top
Commands provided by plugins:

  ps.zeek []                - Show Zeek processes on nodes' systems

Checking Zeek Logs

Zeek will start analyzing traffic according to a default policy and write the log results in /opt/zeek/logs/current directory.

ls -1 /opt/zeek/logs/current/

Some logs that are worth explicit mention:

  • conn.log: Contains an entry for every connection seen on the wire, with basic properties such as time and duration, originator and responder IP addresses, services and ports, payload size, and much more. This log provides a comprehensive record of the network’s activity.
  • notice.log: Identifies specific activity that Zeek recognizes as potentially interesting, odd, or bad. Such activity is called a “notice”.
  • known_services.log: This log file contains the services detected on the local network and are known to be actively used by the clients on the network. It helps in enumerating what all services are observed on a local network and if they all are intentional and known to the network administrator.
  • weird.log: Contains unusual or exceptional activity that can indicate malformed connections, traffic that doesn’t conform to a particular protocol, malfunctioning or misconfigured hardware/services, or even an attacker attempting to avoid/confuse a sensor.
  • (protocol).log such as (dns.log, dhcp.log, http.log, snmp.log): contains information for packets found in each respective protocol.

Sample conn.log logs;

tail /opt/zeek/logs/current/conn.log

1641574281.587589	Cm5WfA3pJ25s3bbZn1	47763	48316	tcp	-	-	-	-	OTH	T	T	0	Cc	00	0	0	-
1641574281.587662	C5Wrln2Yh1Y5PhXZO4	47763	48318	tcp	-	-	-	-	OTH	T	T	0	Cc	00	0	0	-
1641574284.454002	CxnN0kz7NeFf9g5ra	35434	47761	tcp	-	-	-	-	OTH	T	T	0	Cc	00	0	0	-
1641574284.936654	Ch0ywkpEgDkDI4hqk	35432	47761	tcp	-	-	-	-	OTH	T	T	0	Cc	00	0	0	-
1641574287.708293	C2qOcl1vMaYxUaDcU3	47761	35426	tcp	-	-	-	-	OTH	T	T	0	Cc	00	0	0	-
1641574287.708323	CgSooa1flTATHu6N8g	47761	35428	tcp	-	-	-	-	OTH	T	T	0	Cc	00	0	0	-
1641574289.602766	C96gMg3RQgvsbGmp55	47762	46776	tcp	-	-	-	-	OTH	T	T	0	Cc	00	0	0	-
1641574289.602842	CWOj3w2erhdPzHG0d8	47762	46786	tcp	-	-	-	-	OTH	T	T	0	Cc	00	0	0	-
1641574289.602914	CzBzwA4ITDK3ctjVNc	47762	46788	tcp	-	-	-	-	OTH	T	T	0	Cc	00	0	0	-
1641574289.942467	CqoqDG3Bhuq7hrLeed	35432	47761	tcp	-	-	-	-	OTH	T	T	0	Cc	00	0	0

The fields and types are;

#fields	ts	uid	id.orig_h	id.orig_p	id.resp_h	id.resp_p	proto	service	duration	orig_bytes	resp_bytes	conn_state	local_orig	local_resp	missed_bytes	history	orig_pkts	orig_ip_bytes	resp_pkts	resp_ip_bytes	tunnel_parents
#types	time	string	addr	port	addr	port	enum	string	interval	count	count	string	bool	bool	count	string	count	count	count	count	set[string]

Checking Zeek Node Processes

You can check processes running on each node by executing;

zeekctl ps.zeek <node>

For example, to check processes on Zeek manager node;

zeekctl ps.zeek kifarunix-demo-zeek-manager 

        USER         PID    PPID %CPU %MEM    VSZ   RSS TT       S  STARTED     TIME COMMAND
   (-) root         783     777  0.1 10.2 824476 102352 ?       S 19:21:56 00:00:02 zeek
   (+) root         833     827  0.0 10.1 720236 101692 ?       S 19:21:58 00:00:01 zeek
   (-) root         882     876  0.0  9.9 717956 99360 ?        S 19:22:00 00:00:01 zeek
   (-) root         954     944  0.3 23.3 849108 233028 ?       S 19:22:03 00:00:06 zeek
   (-) root         955     942  0.1 23.1 849696 231068 ?       S 19:22:03 00:00:02 zeek

And that brings us to the end of our tutorial on how to install Zeek on Debian 11.

In our next tutorials, we will learn how to analyze network traffic with Zeek.


Installing Zeek

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