Aug 15

Sniffing on Mikrotik and streaming in real-time to Wireshark

Reading time: 2 – 2 minutes

When you have a Mikrotik in any point of your network and you want to launch a sniffer for debugging or troubleshooting, a part from original RouterOS tools, you can stream captured traffic in real-time to Wireshark and inspect packets there.

The idea is exactly the same like I explained on the entry: Sniffing traffic in a Linux box and streaming in real-time to Wireshark on Windows.

Mikrotik configuration using the web interface is like that:

mikrotik-config

We assume 10.2.0.44 is the IP address of the Wireshark box, ensure that you don’t block UDP traffic on port 37008 because the stream from Mikrotik uses that target port. And define your own filters.

About Wireshark configuration is really simple, just set up the filter to allow only traffic from sniffing stream and select the network interface where traffic comes.

wireshark-config

Previous captures allow us to debug DNS queries to Google DNS service, this is the result when you click to the icon marked with a red circle on previous screen capture.

wireshark-traffic

Apr 12

Sniffing traffic in a Linux box and streaming in real-time to Wireshark on Windows

Reading time: 1 – 2 minutes

Sniffing and inspect complex protocols on “tcpdump” is usually painful. Of course, “tcpflow” is a very useful tool but is not always enough to sniff in a console. Wireshark is always a better option when it’s time to debug and troubleshooting communication problems.

But it’s not always easy to plug a Network TAP where you want to sniff. If at that point we have a Linux box with “ssh” and “tcpdump”. An interesting option is stream sniffed traffic to another box with Wireshark and dissect packet octets in their layers, fields, etc.

When Wireshark box is based on Windows you need “plink.exe“, and you can do thinks like that:

plink.exe -ssh -pw LINUX_BOX_PASSWORD root@LINUX_BOX_IP "tcpdump -n -i INTERFACE_TO_SNIFF -s 0 -w - not port 22" | "%PATH_TO_WIRESHARK\Wireshark.exe" -k -i -

Next you have a screenshot with a real life example of that:

tcpdump_streams_to_wireshark_secure

Jun 13

tcpflow: mirant streams tcp en un moment

Reading time: 1 – 2 minutes

Fins ara per poder seguir un protocol dins del enllaç TCP, o sigui els missatges de la capa 5, sempre acabava capturant-lo amb el wireshark o en el seu defecte amb el tcpdump generava un fitxer .cap que després obria al wireshark i a través d’una funció tan simple com el Follow TCP stream em montava la sessió de capa d’aplciació que podia seguir de forma ben còmode. El gran descobriment que vaig fer l’altre dia és el tcpflow una eina la mar de simple i lleugera que com no podia ser d’altre forma usa les llibreries libpcap, le mateixes que el tcpdump i el wireshark per mostrar-nos de forma completament visual i simple a través de la consola o contra un fitxer el contingut de la sessió TCP. Espero que li tregueu tan profit com jo a l’eina.