|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 184.108.40.206
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 > 220.127.116.11.80: 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)
18.104.22.168.80 > 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 > 22.214.171.124.80: 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 > 126.96.36.199.80: 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)
188.8.131.52.80 > 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)
184.108.40.206.80 > 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.
The BPM world is going through some evolution or changes where traditional business process management solutions really have nowhere to go in terms of development of the road map. In this demo at 15th Cloud Expo, Kyle Hansen, Director of Professional Services at AgilePoint, shows AgilePoint’s unique approach to dealing with this market circumstance by developing a rapid application composition or development framework.
Dec. 19, 2014 04:45 PM EST Reads: 724
“In the past year we've seen a lot of stabilization of WebRTC. You can now use it in production with a far greater degree of certainty. A lot of the real developments in the past year have been in things like the data channel, which will enable a whole new type of application," explained Peter Dunkley, Technical Director at Acision, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 19, 2014 04:00 PM EST Reads: 1,119
The major cloud platforms defy a simple, side-by-side analysis. Each of the major IaaS public-cloud platforms offers their own unique strengths and functionality. Options for on-site private cloud are diverse as well, and must be designed and deployed while taking existing legacy architecture and infrastructure into account. Then the reality is that most enterprises are embarking on a hybrid cloud strategy and programs. In this Power Panel at 15th Cloud Expo (http://www.CloudComputingExpo.com), moderated by Ashar Baig, Research Director, Cloud, at Gigaom Research, Nate Gordon, Director of T...
Dec. 19, 2014 11:30 AM EST Reads: 2,282
"BSQUARE is in the business of selling software solutions for smart connected devices. It's obvious that IoT has moved from being a technology to being a fundamental part of business, and in the last 18 months people have said let's figure out how to do it and let's put some focus on it, " explained Dave Wagstaff, VP & Chief Architect, at BSQUARE Corporation, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 19, 2014 11:00 AM EST Reads: 1,839
SYS-CON Events announced today that Windstream, a leading provider of advanced network and cloud communications, has been named “Silver Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9–11, 2015, at the Javits Center in New York, NY. Windstream (Nasdaq: WIN), a FORTUNE 500 and S&P 500 company, is a leading provider of advanced network communications, including cloud computing and managed services, to businesses nationwide. The company also offers broadband, phone and digital TV services to consumers primarily in rural areas.
Dec. 19, 2014 07:00 AM EST Reads: 2,153
The Internet of Things is not new. Historically, smart businesses have used its basic concept of leveraging data to drive better decision making and have capitalized on those insights to realize additional revenue opportunities. So, what has changed to make the Internet of Things one of the hottest topics in tech? In his session at @ThingsExpo, Chris Gray, Director, Embedded and Internet of Things, discussed the underlying factors that are driving the economics of intelligent systems. Discover how hardware commoditization, the ubiquitous nature of connectivity, and the emergence of Big Data a...
Dec. 19, 2014 06:30 AM EST Reads: 2,144
ARMONK, N.Y., Nov. 20, 2014 /PRNewswire/ -- IBM (NYSE: IBM) today announced that it is bringing a greater level of control, security and flexibility to cloud-based application development and delivery with a single-tenant version of Bluemix, IBM's platform-as-a-service. The new platform enables developers to build ap...
Dec. 19, 2014 05:00 AM EST Reads: 1,957
SYS-CON Events announced today that IDenticard will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. IDenticard™ is the security division of Brady Corp (NYSE: BRC), a $1.5 billion manufacturer of identification products. We have small-company values with the strength and stability of a major corporation. IDenticard offers local sales, support and service to our customers across the United States and Canada. Our partner network encompasses some 300 of the world's leading systems integrators and security s...
Dec. 19, 2014 04:00 AM EST Reads: 1,956
DevOps Summit 2015 New York, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that it is now accepting Keynote Proposals. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long development cycles that produce software that is obsolete at launch. DevOps may be disruptive, but it is essential.
Dec. 18, 2014 09:45 PM EST Reads: 983
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 18, 2014 09:00 AM EST Reads: 1,270
Nigeria has the largest economy in Africa, at more than US$500 billion, and ranks 23rd in the world. A recent re-evaluation of Nigeria's true economic size doubled the previous estimate, and brought it well ahead of South Africa, which is a member (unlike Nigeria) of the G20 club for political as well as economic reasons. Nigeria's economy can be said to be quite diverse from one point of view, but heavily dependent on oil and gas at the same time. Oil and natural gas account for about 15% of Nigera's overall economy, but traditionally represent more than 90% of the country's exports and as...
Dec. 18, 2014 06:00 AM EST Reads: 803
The Internet of Things is a misnomer. That implies that everything is on the Internet, and that simply should not be - especially for things that are blurring the line between medical devices that stimulate like a pacemaker and quantified self-sensors like a pedometer or pulse tracker. The mesh of things that we manage must be segmented into zones of trust for sensing data, transmitting data, receiving command and control administrative changes, and peer-to-peer mesh messaging. In his session at @ThingsExpo, Ryan Bagnulo, Solution Architect / Software Engineer at SOA Software, focused on desi...
Dec. 17, 2014 11:15 PM EST Reads: 1,309
"At our booth we are showing how to provide trust in the Internet of Things. Trust is where everything starts to become secure and trustworthy. Now with the scaling of the Internet of Things it becomes an interesting question – I've heard numbers from 200 billion devices next year up to a trillion in the next 10 to 15 years," explained Johannes Lintzen, Vice President of Sales at Utimaco, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 17, 2014 11:00 PM EST Reads: 1,369
"For over 25 years we have been working with a lot of enterprise customers and we have seen how companies create applications. And now that we have moved to cloud computing, mobile, social and the Internet of Things, we see that the market needs a new way of creating applications," stated Jesse Shiah, CEO, President and Co-Founder of AgilePoint Inc., in this SYS-CON.tv interview at 15th Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 17, 2014 08:00 PM EST Reads: 1,343
SYS-CON Events announced today that Gridstore™, the leader in hyper-converged infrastructure purpose-built to optimize Microsoft workloads, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Gridstore™ is the leader in hyper-converged infrastructure purpose-built for Microsoft workloads and designed to accelerate applications in virtualized environments. Gridstore’s hyper-converged infrastructure is the industry’s first all flash version of HyperConverged Appliances that include both compute and storag...
Dec. 17, 2014 06:30 PM EST Reads: 1,245
Today’s enterprise is being driven by disruptive competitive and human capital requirements to provide enterprise application access through not only desktops, but also mobile devices. To retrofit existing programs across all these devices using traditional programming methods is very costly and time consuming – often prohibitively so. In his session at @ThingsExpo, Jesse Shiah, CEO, President, and Co-Founder of AgilePoint Inc., discussed how you can create applications that run on all mobile devices as well as laptops and desktops using a visual drag-and-drop application – and eForms-buildi...
Dec. 17, 2014 11:45 AM EST Reads: 1,471
We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
Dec. 16, 2014 11:45 PM EST Reads: 1,310
Code Halos - aka "digital fingerprints" - are the key organizing principle to understand a) how dumb things become smart and b) how to monetize this dynamic. In his session at @ThingsExpo, Robert Brown, AVP, Center for the Future of Work at Cognizant Technology Solutions, outlined research, analysis and recommendations from his recently published book on this phenomena on the way leading edge organizations like GE and Disney are unlocking the Internet of Things opportunity and what steps your organization should be taking to position itself for the next platform of digital competition.
Dec. 15, 2014 11:45 PM EST Reads: 1,672
The 3rd International Internet of @ThingsExpo, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that its Call for Papers is now open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
Dec. 15, 2014 10:30 AM EST Reads: 6,876
As the Internet of Things unfolds, mobile and wearable devices are blurring the line between physical and digital, integrating ever more closely with our interests, our routines, our daily lives. Contextual computing and smart, sensor-equipped spaces bring the potential to walk through a world that recognizes us and responds accordingly. We become continuous transmitters and receivers of data. In his session at @ThingsExpo, Andrew Bolwell, Director of Innovation for HP's Printing and Personal Systems Group, discussed how key attributes of mobile technology – touch input, sensors, social, and ...
Dec. 15, 2014 10:00 AM EST Reads: 1,956