|By Hurricane Labs||
|March 20, 2012 04:12 PM EDT||
The Ins and Outputs of TCPDUMP
By: Nicholas Beris
As a Network Engineer, I spend a lot of time on, in, and around the terminal. Many of the systems that I work with are remote and taking the time to download a packet capture in the middle of an emergency call and waiting for Wireshark to get the necessary details is just too much of a hassle. (Plus, it makes me feel like I’m an operator in the Matrix with the scrolling code.) Now don’t get me wrong, Wireshark is a great tool and has many uses, but a lot of times it’s just not practical. Besides, are you really going to download the packets from a snort alert and pump them into Wireshark? This my friends is where Tcpdump comes into play and shines.
What is Tcpdump?
Tcpdump is the most commonly and widely used tool to analyze and intercept various types of Ethernet traffic. A network administrator, security auditor, or anyone else dealing in the end to end connectivity of their infrastructure will find this tool pre-installed most of time. Many times when working with third party vendors, sometimes you have to prove that its isn’t your network, firewall, or NAT causing the issue with the application and its just poor coding on their end.
First we will look at some simple traffic and in this case will be an apt install of 2 packages.
The following is the command that I used to to ‘capture’ or record this network traffic.
tcpdump -s 1500 -Avvvn -i wlan0 -w package.pcap host 22.214.171.124
tcpdump: Name of the application.
-s 1500: Snap length is how much of the packet to get. The default is 65535 bytes. Setting the snap length to 0 sets it to it’s default. (According to the man page for my version)
-A: Prints the packet in ASCII. Useful for plain text traffic and application troubleshooting.
-vvv: Very very verbose – Prints more information about the packet such as TTL and a lot more
-n: Won’t convert address to human names
-i: Which interface to listen and capture on
-w: Write the packet to said file name
host: The remote peer
Now that we have successfully written the packets to a file we can now analyze the traffic. In any type of troubleshooting situation you have to start at square one. Lets open this file and pipe it into something useful instead of filling the scroll back buffer and missing the first essential connection details.
Since the TCP/IP stack has retransmission as part of the protocol if the first few packets fail then the rest of the connection is doomed.
tcpdump -s 1500 -Avvvn -r package.pcap | less
The -r switch reads the file instead of writing it. Since we already filtered out any other traffic with the host argument we don’t need to be as detailed in our command. The | (pipe) means direct the standard output (console screen) to another application, in the case “less”. This give us the ability to scroll through the whole .pcap file.
The first the 3 packets represent the 3 way-handshake which every TCP connection must go through to set up the connection.
12:26:58.632628 IP (tos 0x0, ttl 64, id 20547, offset 0, flags [DF]
, proto TCP (6), length 60)
10.0.1.38.59181 > 126.96.36.199.80: Flags [S], cksum 0xb5e9 (cor
rect), seq 1526109302, win 5840, options [mss 1460,sackOK,TS val 68
00437 ecr 0,nop,wscale 7], length 0
12:26:58.663268 IP (tos 0x0, ttl 51, id 0, offset 0, flags [DF], pr
oto TCP (6), length 60)
188.8.131.52.80 > 10.0.1.38.59181: Flags [S.], cksum 0x7075 (co
rrect), seq 2554095472, ack 1526109303, win 5792, options [mss 1460
,sackOK,TS val 2580458519 ecr 6800437,nop,wscale 7], length 0
12:26:58.663321 IP (tos 0x0, ttl 64, id 20548, offset 0, flags [DF]
, proto TCP (6), length 52)
10.0.1.38.59181 > 184.108.40.206.80: Flags [.], cksum 0xb5ab (cor
rect), ack 1, win 46, options [nop,nop,TS val 6800445 ecr 258045851
9], length 0
And now my host is sending its HTTP GET request to the remote HTTP server. Remember when I said in the beginning that I was going to install two packages? Well you can see two GET requests made to the server in the output below. Can you tell what I was installing?
12:26:58.663524 IP (tos 0x0, ttl 64, id 20549, offset 0, flags [DF]
, proto TCP (6), length 435)
10.0.1.38.59181 > 220.127.116.11.80: Flags [P.], cksum 0x0d68 (correct), seq 1:384, ack 1, win 46, options [nop,nop,TS val 6800445 ecr 2580458519], length 383
User-Agent: Debian APT-HTTP/1.3 (0.8.10.3)
GET /debian/pool/main/a/awn-extras-applets/awn-applets-python-extras_0.4.0-3_all.deb HTTP/1.1
User-Agent: Debian APT-HTTP/1.3 (0.8.10.3)
How do we know that the server even received our request? TCP will always send an ACK, or in the case of a corrupt packet, a reset (RST) the last packet. As you can see in the following output there is the acknowledge of the GET request and then the server’s HTTP 200 OK response.
12:26:58.693420 IP (tos 0x0, ttl 51, id 52036, offset 0, flags [DF]
, proto TCP (6), length 52)
18.104.22.168.80 > 10.0.1.38.59181: Flags [.], cksum 0xb406 (cor
rect), ack 384, win 54, options [nop,nop,TS val 2580458549 ecr 6800
445], length 0
12:26:58.750220 IP (tos 0x0, ttl 51, id 52037, offset 0, flags [DF]
, proto TCP (6), length 1500)
22.214.171.124.80 > 10.0.1.38.59181: Flags [.], seq 1:1449, ack 3
84, win 54, options [nop,nop,TS val 2580458605 ecr 6800445], length
Date: Sun, 18 Mar 2012 16:27:03 GMT
Server: Apache/2.2.3 (CentOS)
Last-Modified: Mon, 19 Jul 2010 07:02:03 GMT
Content-Type: text/plain; charset=UTF-8
And as they say “the rest is history”. Well, technically the rest is of the TCP stream for my packages, but if you are troubleshooting further than the initial connections you are going to need to roll up your sleeves and have a firm grasp of the TCP protocol. If you’re not as strong at reading packet captures or understanding how the whole TCP/IP stacks work, then this is the best way to learn with simple, easy to define and read traffic. In my next entry I plan on going more in depth with situational examples.
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management...
Feb. 7, 2016 03:30 PM EST Reads: 376
The cloud promises new levels of agility and cost-savings for Big Data, data warehousing and analytics. But it’s challenging to understand all the options – from IaaS and PaaS to newer services like HaaS (Hadoop as a Service) and BDaaS (Big Data as a Service). In her session at @BigDataExpo at @ThingsExpo, Hannah Smalltree, a director at Cazena, will provide an educational overview of emerging “as-a-service” options for Big Data in the cloud. This is critical background for IT and data profes...
Feb. 7, 2016 02:45 PM EST Reads: 144
SYS-CON Events announced today that VAI, a leading ERP software provider, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. VAI (Vormittag Associates, Inc.) is a leading independent mid-market ERP software developer renowned for its flexible solutions and ability to automate critical business functions for the distribution, manufacturing, specialty retail and service sectors. An IBM Premier Business Part...
Feb. 7, 2016 02:00 PM EST Reads: 563
SYS-CON Events announced today that Alert Logic, Inc., the leading provider of Security-as-a-Service solutions for the cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Alert Logic, Inc., provides Security-as-a-Service for on-premises, cloud, and hybrid infrastructures, delivering deep security insight and continuous protection for customers at a lower cost than traditional security solutions. Ful...
Feb. 7, 2016 01:45 PM EST Reads: 366
Fortunately, meaningful and tangible business cases for IoT are plentiful in a broad array of industries and vertical markets. These range from simple warranty cost reduction for capital intensive assets, to minimizing downtime for vital business tools, to creating feedback loops improving product design, to improving and enhancing enterprise customer experiences. All of these business cases, which will be briefly explored in this session, hinge on cost effectively extracting relevant data from ...
Feb. 7, 2016 01:30 PM EST
With the Apple Watch making its way onto wrists all over the world, it’s only a matter of time before it becomes a staple in the workplace. In fact, Forrester reported that 68 percent of technology and business decision-makers characterize wearables as a top priority for 2015. Recognizing their business value early on, FinancialForce.com was the first to bring ERP to wearables, helping streamline communication across front and back office functions. In his session at @ThingsExpo, Kevin Roberts...
Feb. 7, 2016 12:00 PM EST Reads: 347
SYS-CON Events announced today that Interoute, owner-operator of one of Europe's largest networks and a global cloud services platform, has been named “Bronze Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2015 at the Javits Center in New York, New York. Interoute is the owner-operator of one of Europe's largest networks and a global cloud services platform which encompasses 12 data centers, 14 virtual data centers and 31 colocation centers, with connections to 195 ad...
Feb. 7, 2016 11:30 AM EST Reads: 349
With an estimated 50 billion devices connected to the Internet by 2020, several industries will begin to expand their capabilities for retaining end point data at the edge to better utilize the range of data types and sheer volume of M2M data generated by the Internet of Things. In his session at @ThingsExpo, Don DeLoach, CEO and President of Infobright, will discuss the infrastructures businesses will need to implement to handle this explosion of data by providing specific use cases for filte...
Feb. 7, 2016 10:15 AM EST Reads: 120
As enterprises work to take advantage of Big Data technologies, they frequently become distracted by product-level decisions. In most new Big Data builds this approach is completely counter-productive: it presupposes tools that may not be a fit for development teams, forces IT to take on the burden of evaluating and maintaining unfamiliar technology, and represents a major up-front expense. In his session at @BigDataExpo at @ThingsExpo, Andrew Warfield, CTO and Co-Founder of Coho Data, will dis...
Feb. 7, 2016 07:00 AM EST Reads: 125
SYS-CON Events announced today that Fusion, a leading provider of cloud services, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Fusion, a leading provider of integrated cloud solutions to small, medium and large businesses, is the industry's single source for the cloud. Fusion's advanced, proprietary cloud service platform enables the integration of leading edge solutions in the cloud, including clou...
Feb. 6, 2016 03:30 PM EST Reads: 724
Most people haven’t heard the word, “gamification,” even though they probably, and perhaps unwittingly, participate in it every day. Gamification is “the process of adding games or game-like elements to something (as a task) so as to encourage participation.” Further, gamification is about bringing game mechanics – rules, constructs, processes, and methods – into the real world in an effort to engage people. In his session at @ThingsExpo, Robert Endo, owner and engagement manager of Intrepid D...
Feb. 5, 2016 09:00 PM EST Reads: 789
Eighty percent of a data scientist’s time is spent gathering and cleaning up data, and 80% of all data is unstructured and almost never analyzed. Cognitive computing, in combination with Big Data, is changing the equation by creating data reservoirs and using natural language processing to enable analysis of unstructured data sources. This is impacting every aspect of the analytics profession from how data is mined (and by whom) to how it is delivered. This is not some futuristic vision: it's ha...
Feb. 2, 2016 02:00 PM EST Reads: 414
WebRTC has had a real tough three or four years, and so have those working with it. Only a few short years ago, the development world were excited about WebRTC and proclaiming how awesome it was. You might have played with the technology a couple of years ago, only to find the extra infrastructure requirements were painful to implement and poorly documented. This probably left a bitter taste in your mouth, especially when things went wrong.
Feb. 2, 2016 04:30 AM EST Reads: 853
Learn how IoT, cloud, social networks and last but not least, humans, can be integrated into a seamless integration of cooperative organisms both cybernetic and biological. This has been enabled by recent advances in IoT device capabilities, messaging frameworks, presence and collaboration services, where devices can share information and make independent and human assisted decisions based upon social status from other entities. In his session at @ThingsExpo, Michael Heydt, founder of Seamless...
Feb. 1, 2016 05:00 AM EST Reads: 941
The IoT's basic concept of collecting data from as many sources possible to drive better decision making, create process innovation and realize additional revenue has been in use at large enterprises with deep pockets for decades. So what has changed? In his session at @ThingsExpo, Prasanna Sivaramakrishnan, Solutions Architect at Red Hat, discussed the impact commodity hardware, ubiquitous connectivity, and innovations in open source software are having on the connected universe of people, thi...
Jan. 31, 2016 09:00 PM EST Reads: 729
WebRTC: together these advances have created a perfect storm of technologies that are disrupting and transforming classic communications models and ecosystems. In his session at WebRTC Summit, Cary Bran, VP of Innovation and New Ventures at Plantronics and PLT Labs, provided an overview of this technological shift, including associated business and consumer communications impacts, and opportunities it may enable, complement or entirely transform.
Jan. 31, 2016 07:15 PM EST Reads: 1,148
There are so many tools and techniques for data analytics that even for a data scientist the choices, possible systems, and even the types of data can be daunting. In his session at @ThingsExpo, Chris Harrold, Global CTO for Big Data Solutions for EMC Corporation, showed how to perform a simple, but meaningful analysis of social sentiment data using freely available tools that take only minutes to download and install. Participants received the download information, scripts, and complete end-t...
Jan. 31, 2016 10:00 AM EST Reads: 1,221
For manufacturers, the Internet of Things (IoT) represents a jumping-off point for innovation, jobs, and revenue creation. But to adequately seize the opportunity, manufacturers must design devices that are interconnected, can continually sense their environment and process huge amounts of data. As a first step, manufacturers must embrace a new product development ecosystem in order to support these products.
Jan. 31, 2016 10:00 AM EST Reads: 815
Manufacturing connected IoT versions of traditional products requires more than multiple deep technology skills. It also requires a shift in mindset, to realize that connected, sensor-enabled “things” act more like services than what we usually think of as products. In his session at @ThingsExpo, David Friedman, CEO and co-founder of Ayla Networks, discussed how when sensors start generating detailed real-world data about products and how they’re being used, smart manufacturers can use the dat...
Jan. 30, 2016 07:45 PM EST Reads: 792
When it comes to IoT in the enterprise, namely the commercial building and hospitality markets, a benefit not getting the attention it deserves is energy efficiency, and IoT’s direct impact on a cleaner, greener environment when installed in smart buildings. Until now clean technology was offered piecemeal and led with point solutions that require significant systems integration to orchestrate and deploy. There didn't exist a 'top down' approach that can manage and monitor the way a Smart Buildi...
Jan. 30, 2016 03:45 PM EST Reads: 1,271