Wireshark 1.12 has just arrived, and of course the first thing to do is to download and install the new version. The second thing to do should be to read the release notes.Nobody seems to do it, but everybody should. Okay, before I get to the TCP expert thing, let’s see why release notes are important.
I was sitting in the back in Landis TCP Reassembly talk at Sharkfest 2014 (working on my slides for my next talk) when at the end one of the attendees approached me and asked me to explain determining TCP initial RTT to him again. I asked him for a piece of paper and a pen, and coached him through the process. This is what I did.
Probably the most common way of capturing network data is not a decision between SPAN or TAP – it is Wireshark simply being installed on one of the computers that need to be analyzed. While this an easy way to capture network packets it is also an easy way to get “wrong” results, because there are a lot of side effects when capturing packets directly on a computer. I discussed a lot of these side effects in my Sharkfest 2013 talk “PA-14: Top 5 False Positives” already, but let’s go check them out again.
A few days ago, Olli, one of our team members, sent me a funny trace that he’d taken while configuring the security settings on a Netoptics Bypass kit. This device has an SNMP and HTTP management service, and when he disabled the HTTP service he verified if the setting was accepted (like you should). Usually, there would either be a Reset packet coming back when a SYN is sent, or no answer at all. To his surprise, the device behaved a little different than expected.
It’s a funny thing about using Wireshark – I think I am pretty good at using it in an efficient way, but there are always some new tricks that I learn every once in a while.
The Multi IP layer problem
For a current IPS/IDS project I was looking for a test system to benchmark various IDS/IPS engines. The idea was to record network captures carrying malware samples in HTTP, SMTP or other protocols, and replaying them against the various detection engines. Problem with that is that tools like tcpreplay, bittwist or Ostinato all replay the trace on a single network card, which means that both “client” and “server” side of the communication are injected into the same NIC of the detection engine.