Hello Laci,

Question: I can successfully read the logs of the firewall that is located in the same network that my logserver is, but the second firewall is sending the logs from a different network segment to the log server. Does this causes the problem? Again: I can see the traffic on my network interface, but netcat doesn’t receive anything on port 514 (for the second firewall). Does iptables fools me somehow?

Mit freundlichen Grüßen / Best regards

Benjamin Bruns

IT Security Manager

CYPP GmbH

Gotenstrasse 15

20097 Hamburg

Germany

Telefon: +49 40 237 34-285

Mobil: +49 160 3230 655

Mail: benjamin.bruns@cypp.de

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Von: syslog-ng <syslog-ng-bounces@lists.balabit.hu> Im Auftrag von Laszlo Szemere (lszemere)
Gesendet: Freitag, 28. August 2020 13:41
An: Syslog-ng users' and developers' mailing list <syslog-ng@lists.balabit.hu>
Betreff: Re: [syslog-ng] syslog-ng is ignoring a network source

Hello Ben,

nc -u -l -p 514

-u : use UDP

-l : listen in server mode, instead of sending

-p : defines port number

(If you need, you can also specify the local IP address to bind to with the -s option.)

Br,

Laci

From: syslog-ng <syslog-ng-bounces@lists.balabit.hu> on behalf of Bruns, Benjamin <Benjamin.Bruns@cypp.de>
Sent: Friday, August 28, 2020 13:29
To: Syslog-ng users' and developers' mailing list <syslog-ng@lists.balabit.hu>
Subject: Re: [syslog-ng] syslog-ng is ignoring a network source

CAUTION: This email originated from outside of the organization. Do not follow guidance, click links, or open attachments unless you recognize the sender and know the content is safe.

Hello Laci,

how do I check that by using netcat?

Cheers, Ben

Von: syslog-ng <syslog-ng-bounces@lists.balabit.hu> Im Auftrag von Laszlo Szemere (lszemere)
Gesendet: Freitag, 28. August 2020 12:21
An: Syslog-ng users' and developers' mailing list <syslog-ng@lists.balabit.hu>
Betreff: Re: [syslog-ng] syslog-ng is ignoring a network source

Hello Ben,

our experience shows that having logs in Wireshark doesn't necessary means that they reach the applications. (Wireshark captures packets on the interface level.)

So as a first step I would recommend to clarify that the logs from the second host indeed reaches Syslog-ng. (For UDP logs netcat usually is enough.)

Once it is clear that those logs reaches the application level, we can focus on debugging Syslog-ng.

By starting Syslog-ng with the following options, it would be much easier to examine the flow of messages:

syslog-ng -Fdevt

-F : start it in the foreground

-d : debug mode

-e : log messages to stderr

-v : increases verbository

-t : also enable trace messages

Note: With these options enabled, Syslog-ng will produce a LOT of messages. So if you can turn off other logging sources temporary, than it will be much more easier to read those logs.

At this point you should start to receive this kind of debug messages, which will indicate that Syslog-ng received the log messages from your host:

[2020-08-28T10:09:43.289660] Incoming log entry; line='hello world'

From this point the easiest way is to start with a minimal config, and build up your final configuration step by step. Checking incoming logs in each steps.

Br,

Laci

From: syslog-ng <syslog-ng-bounces@lists.balabit.hu> on behalf of Bruns, Benjamin <Benjamin.Bruns@cypp.de>
Sent: Friday, August 28, 2020 11:53
To: syslog-ng@lists.balabit.hu <syslog-ng@lists.balabit.hu>
Subject: [syslog-ng] syslog-ng is ignoring a network source

CAUTION: This email originated from outside of the organization. Do not follow guidance, click links, or open attachments unless you recognize the sender and know the content is safe.

Hello!

I try to send syslogs from two firewalls to my syslog-ng host. The first one worked immediately, but logs of the second firewall seems to be ignored. Both syslogs come in via UDP on port 514 and I can see them in Wireshark on my syslog-ng host, but they disappear for my second firewall in a black hole. Both have Logstash as their destination configured. Any ideas? Thanks in advance!

Cheers, Ben