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Elastic SIEM 7 Part II - Logstash to monitor Cisco Switches Syslog

Logstash logo

Now that our Elastic SIEM is ready to go we can start to monitor some elements. I will start here with my Cisco Small Business/SG switches.

The Switches will use the syslog protocol to send infomations to logstash module.

Logstash will get the message, extracts and parses usefull informations then send them to Elasticsearch.

Understanding Logstash

SIEM | logstash Input Filter and Output modules
Logstash, pipeline processing.

Installing Logstash (Debian Server)

I'll install Logstash on the same machine than the Elasticsearch engine.

Installing From raw packages (dpkg)

  • Download Logstash package and the associate sha512 message diges to /tmp/ :
root@host:~# wget -P /tmp/
  • Install and enable Logstash :
root@host:~# dpkg -i /tmp/logstash-7.12.0-amd64.deb
root@host:~# systemctl enable logstash.service

Installing From Package Managers (apt)

If you have not yet imported Elasticsearch PGP key and add repository definition yet, see part I.

  • Install and enable Logstash :
root@host:~# apt install logstash


  • Check logstash service :
root@host:~# systemctl status logstash.service
  • Enable logstash at boot :
root@host:~# systemctl enable logstash.service

Logs file

  • Logstash :
root@host:~# tail /var/log/logstash/logstash-plain.log


Pipeline files

Pipeline configuration files will define the stages of our Logstash processing pipeline. The pipeline configuration files are in the /etc/logstash/conf.d directory.


  • Create /etc/logstash/conf.d/cisco.conf file :
input {
	udp {
		port => "514"
		type => "syslog-udp-cisco"

filter {
	grok {  
		#Remember, the syslog message looks like this : <190>%LINK-I-Up: gi1/0/13
		match => { "message" => "^<%{POSINT:syslog_facility}>%%{DATA:cisco_code}: %{GREEDYDATA:syslog_message}" }
output {
	elasticsearch {
		hosts           => [""]
		index           => "cisco-switches-%{+YYYY.MM.dd}"

Pipeline file : explained and detailed

As we can see above, the logstash file consists of three parts : input, filter and output.


Here we simply declare on which port we will listen our syslog frames.

  • UDP protocol :
udp {
  • Specify the port number to listen to :
port => "514"
  • Add syslog-udp-cisco tag to matched rule (it will also be shown on output) :
type => "syslog-udp-cisco"

This is the hard part of our Logstash configuration. It is where we will extract useful informations from our frames. The goal is to split each messages into several parts.

For example with our Cisco syslog messages look like this : «<190>%LINK-I-Up: gi1/0/13» so we would like to split it like this : <syslog_facility>%Cisco Action: Message.

Elasticsearch | logstash Filter explained
  • Good to know the commonly used patterns :
    • WORD : pattern matching a single word
    • NUMBER : pattern matching a positive or negative integer or floating-point number
    • POSINT : pattern matching a positive integer
    • IP : pattern matching an IPv4 or IPv6 IP address
    • NOTSPACE : pattern matching anything that is not a space
    • SPACE : pattern matching any number of consecutive spaces
    • DATA : pattern matching a limited amount of any kind of data
    • GREEDYDATA : pattern matching all remaining data

Once we have our data correctly organized we can send them to our Elasticsearch server.

  • Specify our address :
hosts           => [""]
  • Set index in order to give a correct name to our datas :
index           => "cisco-switches-%{+YYYY.MM.dd}"

Cisco Switches

  • We need to configure our switches to enable logging and precise the ip address of our Logstash server :
Switch(config)# logging host port 514


Check pipeline file

  • If we want to check our pipeline file :
root@host:~# /usr/share/logstash/bin/logstash -f /etc/logstash/conf.d/pipeline.conf --config.test_and_exit

Manually test a pipeline output

  • Stop logstash service :
root@host:~# systemctl stop logstash.service
  • Add listening port and stdout to your pipeline file, in order to watch output on console :
input {
	tcp {
		port => "514"
		type => "syslog-tcp-telnet"

output {
	stdout { codec => rubydebug }
  • Run logstash :
root@host:~# /usr/share/logstash/bin/logstash -f /etc/logstash/conf.d/cisco.conf --config.reload.automatic
  • Use telnet to connect to your logstash listening port (only work with TCP protocol) :
root@host:~# telnet 514
<190>%LINK-I-Up: gi1/0/13

List indexes

Now that our switches are properly configured we can check that there are well recorded in our elasticsearch database.

  • To do so :
root@host:~# curl 'localhost:9200/_cat/indices?v'
health status index                             uuid                   pri rep docs.count docs.deleted store.size
green  open   .apm-agent-configuration          rkV4oelEQzC7zJ19_NYbcw   1   0          0            0       208b           208b
green  open   .kibana_1                         rtWr4Pk-TKmYrQ_jQ7Oi4Q   1   0       1689           93      2.6mb          2.6mb
green  open   .apm-custom-link                  Yo72Y9STSAiuSUWT40AJnw   1   0          0            0       208b           208b
green  open   .kibana_task_manager_1            o_uGNd0mQSu6X5_th3P2ng   1   0          5        50053      4.5mb          4.5mb
green  open   .async-search                     3RGoSaTXRLizPMce1I169w   1   0          3            6       10kb           10kb
yellow open   cisco-switches-2021.04.12         gs_PaI2iT_CMQhABskEB6g   1   1      17109            0      1.5mb          1.5mb
green  open   .kibana-event-log-7.10.2-000002   r_1sdbv0QW2XNR0bcvZN2g   1   0          1            0      5.6kb          5.6kb
yellow open   cisco-switches-2021.04.11         j9yz1SWzRwaG_int0rX4YQ   1   1       2283            0    338.1kb        338.1kb
  • Print index content :
root@host:~# curl -XGET 'localhost:9200/cisco-switches-2021.04.11/_search?pretty&q=response=200'
        "_index" : "cisco-switches-2021.04.11",
        "_type" : "_doc",
        "_id" : "1XV3wngBMGalcfKW8ROi",
        "_score" : 3.052513,
        "_source" : {
          "syslog_message" : "PnP Response Success",
          "@timestamp" : "2021-04-11T19:45:43.739Z",
          "message" : "<190>%PNPAGENT-I-RESPSUCCESS: PnP Response Success",
          "host" : "",
          "type" : "syslog-udp-cisco",
          "cisco_code" : "PNPAGENT-I-RESPSUCCESS",
          "syslog_facility" : "190",
          "@version" : "1"


Check indices

Now that we have our data inside indexes it's time to create a dashboard in kibana to have a graphical view of our swicthes logs.

  • Open Firefox and go to http://KIBANA_IP_SERVER:5601/ address
  • Open main menu and go to Management > Stack Management :
Kibana | Main menu, Management, Stack Management
  • From Stack Management go to Data > Index Management :
Kibana | Main menu, Management, Stack Management, Data, Index Management
  • You should see your indices :
Kibana | Indices

Create index pattern

We will create an index pattern which will match our cisco data sources.

  • Go to main menu and go to Management > Stack Management > Index Patterns :
  • Click Create index pattern :
  • Type «cisco-switches-» to match all data sources :
  • Select «@timestamp» as time filed and click Create index pattern :

Create dashboard

We now have everything to make beautiful graphs.


  • Open main menu and go to Kibana > Dashboard :
  • From there click Create dashboard :
  • Click Create new to create object :
  • Click Lens :
  • Search for cisco-switches :
  • Select Pie as chart type :
  • Click and drop fields host.keyword and cisco_code.keyword :
  • You should see this beautiful Pie, click Save :
  • Give a Title and click Save and return :
  • Now you can see the Pie on your Dashboard :


  • From dashboard click Create new :
  • Click Lens :
  • Select Data table as chart type :
  • Click and drop fields host.keyword, syslog_message.keyword and cisco_code.keyword :
  • You should see this beautiful Data table, click Save :
  • Give a Title and click Save and return :
  • Now Save your Dashboard to keep changes :
  • Give a Title and click Save :
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