|By David Dodd||
|May 22, 2012 10:08 AM EDT||
To capture, parse, and analyze traffic tcpdump is a very powerful tool. To begin a basic capture uses the following syntax.
tcpdump -n –i <interface> -s <snaplen>
-n tells tcpdump to not resolve IP addresses to domain names and port numbers to service names.
-I <interface> tells tcpdump which interface to use.
-s <snaplen> tells tcpdump how much of the packet to record. I used 1515 but 1514 is sufficient for most cases. If you don’t specify a size then it will only capture the first 68 bytes of each packet. A snaplen value of 0 which will use the required length to catch whole packets can be used except for older versions of tcpdump.
Below is an example output of a dump, although it only contains a few lines it holds much information.
12:24:51.517451 IP 10.10.253.34.2400 > 188.8.131.52.53: 54517 A? www.bluecoast.com. (34)
12:24:51:517451 represent the time
10.10.253.34.2400 Source address and port
> Traffic direction
184.108.40.206.53 Destination address and port
54517 ID number that is shared by both the DNS server 220.127.116.11 and 10.10.253.34
A? 10.10.253.34 asks a question regarding the A record for www.bluecoat.com
(34) The entire packet is 34 bytes long.
More tcpdump capture options
Here are some examples of options to use when capturing data and why to use them:
-I specify an interface; this will ensure that you are sniffing where you expect to sniff.
-n tells tcpdump not to resolve IP addresses to domain names and port numbers to service names
-nn don’t resolve hostnames or port names
-X Show packet’s contents in both hex and ASCII
-XX Include Ethernet header
-v Increase verbose –vv –vvv more info back
-c Only get x number of packets and stop
-s tell tcpdump how much of the packet to record
-S print absolute sequence numbers
-e get Ethernet header
-q show less protocol info
-E Decrypt IPSEC traffic by providing an encryption key
Packet, Segment, and Datagram
TCP accepts data from a data stream, segments it into chucks, and adds a TCP header creating a TCP segment. UDP sends messages referred to as a datagram to other hosts on an Internet Protocol (IP) network without requiring prior communications to set up special transmission channels or data paths. Internet Protocol then creates its own datagram out of what it receives from TCP or UDP. If the TCP segment or UDP datagram plus IP’s headers are small enough to send in a single package on the wire then IP creates a packet. If they are too large and exceed the maximum transmission unit (MTU) of the media, IP will fragment the datagram into smaller packets suitable to the MTU. The fragmented packets are then reassembled by the destination.
Tcpdump read and write to/from a file
Tcpdump allows you to write data to a file using the –w option and to read from a file with the –r option.
$ sudo tcpdump -i wlan0 -w dumpfile001
$ sudo tcpdump -r dumpfile.pcap
Some people like to see the files as they are captured and have them saved to a file. Use the following options: tcpdump –n –I eth1 –s 1515 –l | tee output.txt
This option tells tcpdump to make its output line-buffered, while piping the output to the tee utility sends output to the screen and the output.txt simultaneously. This command will display packets on the screen while writing data to an output file output.txt it will not be in binary libpcap format. The best way to do this is run a second instance of tcpdump.
When tcpdump captures packets in libpcap format, it adds a timestamp entry to the record in each packet in the capture file. We can augment that data with the –tttt flag, which adds a date to the timestamp (See Figure #1).
You can use the –tt flag to report the number of seconds and microseconds since the UNIX epoch of 00:00:00 UTC on January 1, 1970. If you are not sure you understand the time difference and need to be absolutely sure of time use the –tt option to show seconds and microseconds since the UNIX epoch (See Figure #2).
Being able to cut the amount of traffic down to just what you are looking for is useful. Here are some useful expressions that can be helpful in tcpdump.
Net – This will capture the traffic on a block of IPs ex 192.168.0.0/24
# tcpdump net 192.168.1.1/24
Src, dst – This will only capture packets form a source or destination.
# tcpdump src 192.168.100.234
# tcpdump dst 10.10.24.56
Host – Capture only traffic based on the IP address
# tcpdump host 10.10.253.34
Proto – Capture works for tcp, udp, and icmp
# tcpdump tcp
Port – Capture packets coming from or going to a port.
# tcpdump port 21
Port ranges – capture packets
# tcpdump port 20-25
Using expressions such as AND [&&], OR [||], & EXCEPT [!]
# tcpdump –n –I eth1 host 10.10.253.34 and host 10.10.33.10
# tcpdump –n –I eht1 src net 10.10.253.0/24 and dst net 10.10.33.0/24 or 18.104.22.168
# tcpdump –n –I eth1 src net 10.10.30.0/24 and not icmp
Searching for info on packets with tcpdump
If you want to search for information in the packet you have to know where to look. Tcpdump starts counting bytes of header information at byte 0 and the 13th byte contains the TCP flags shown in Table #1
Now looking at byte 13 and if the SYN and ACK are set then your binary value would be 00010010 which are the same as decimal 18. We can search for packets looking for this type of data inside byte 13 shown here.
# tcpdump –n –r dumpfile.lpc –c 10 ‘tcp == 18’ and host 172.16.183.2
Here is a sample of what this command will return shown in Figure #3
When capturing data using tcpdump one way to ignore the arp traffic is to put in a filter like so.
# tcpdump –n –s 1515 –c 5 –I eth1 tcp or udp or icmp
This will catch only tcp, udp, or icmp.
If you want to find all the TCP packets with the SYN ACK flag set or other flags set take a look at Table #2 & tcpdump filter syntax shown below.
flag Binary Decimal
URG 00100000 32
ACK 00010000 16
PSH 00001000 8
RST 00000100 4
SYN 00000010 2
FIN 00000001 1
SYNACK 00010010 18
Tcpdump filter syntax
Show all URGENT (URG) packets
# tcpdump ‘tcp == 32’
Show all ACKNOWLEDGE (ACK) packets
# tcpdump ‘tcp == 16’
Show all PUSH (PSH) packets
# tcpdump ‘tcp == 8’
Show all RESET (RST) packets
# tcpdump ‘tcp == 4’
Show all SYNCHRONIZE (SYN) packets
# tcpdump ‘tcp ==2’
Show all FINISH (FIN) packets
# tcpdump ‘tcp == 1’
Show all SYNCHRONIZE/ACKNOWLEDGE (SYNACK) packets
# tcpdump ‘tcp == 18’
Using tcpdump in Incident Response
When doing analysis on network traffic using a tool like tcpdump is critical. Below are some examples of using tcpdump to view a couple of different dump files to learn more about network problems or possible attack scenarios. The first is a binary dump file of a snort log and we are given the following information. The IP address of the Linux system is 192.168.100.45 and an attacker got in using a WU-FTPD vulnerability and deployed a backdoor. What can we find out about how the attack happened and what he did?
First we will take a look at the file
# tcpdump –xX –r snort001.log
The log appears long at this point you may want to run the file in snort
# snort –r snort001.log –A full –c /etc/snort/snort.conf
This will give you some info like total packets processed, protocol breakdown, any alerts, etc. See Figure #4 & #5
Figure #4 Figure #5
Next extract the full snort log file for analysis
# tcpdump –nxX –s 1515 –r snort001.log > tcpdump-full.dat
This will give us a readable file to parse through. After looking through it we find ip-proto-11, which is Network Voice Protocol (NVP) traffic. Now we will search through the file looking for ip-proto-11.
# tcpdump –r snort001.log –w NVP-traffic.log proto 11
This command will read the snort001.log file and look for ‘log proto 11’ and writes the contents to the file NVP-traffic.log. Next we need to be able to view the file because it is a binary file.
# tcpdump –nxX –s 1515 –r NVP-traffic.log > nvp-traffic_log.dat
This will be a file of both hex and ASCII, which is nice but we just want the IP address. Try this.
# tcpdump –r NVP-traffic.log > nvp-traffic_log01.dat
This will give us a list of IP address that were communicating using the Network Voice Protocol (NVP) (See Figure #6).
Next we look at another snort dump file from a compromised windows box that was communicating with an IRC server. What IRC servers did the server at 172.16.134.191 communicate with?
Look for TCP connections originating from the server toward the outside and we can use tcpdump with a filtering expression to capture SYN/ACK packets incoming from outside servers.
# tcpdump -n -nn -r snort_log 'tcp and dst host 172.16.134.191 and tcp==18'
This produces a long list of connections going from 172.16.134.191 to outside connections. (see Figure #7).
Now we know that IRC communicate on port 6666 to 6669 so let’s add that and narrow down the search with the following command.
# tcpdump -n -nn -r snort_log 'tcp and dst host 22.214.171.124 and tcp==18' and portrange 6666-6669 (See output in Figure #8 below)
Now we have narrowed the list down to 3 IP’s that were communicating with the server using IRC.
Tcpdump is a wonderful, general-purpose packet sniffer and incident response tool that should be in your tool shed.
The WebRTC Summit 2014 New York, to be held June 9-11, 2015, at the Javits Center in New York, NY, announces that its Call for Papers is open. Topics include all aspects of improving IT delivery by eliminating waste through automated business models leveraging cloud technologies. WebRTC Summit is co-located with 16th International Cloud Expo, @ThingsExpo, Big Data Expo, and DevOps Summit.
Mar. 28, 2015 01:00 PM EDT Reads: 1,418
@ThingsExpo has been named the Top 5 Most Influential M2M Brand by Onalytica in the ‘Machine to Machine: Top 100 Influencers and Brands.' Onalytica analyzed the online debate on M2M by looking at over 85,000 tweets to provide the most influential individuals and brands that drive the discussion. According to Onalytica the "analysis showed a very engaged community with a lot of interactive tweets. The M2M discussion seems to be more fragmented and driven by some of the major brands present in the M2M space. This really allows some room for influential individuals to create more high value inter...
Mar. 28, 2015 12:45 PM EDT Reads: 4,588
The world's leading Cloud event, Cloud Expo has launched Microservices Journal on the SYS-CON.com portal, featuring over 19,000 original articles, news stories, features, and blog entries. DevOps Journal is focused on this critical enterprise IT topic in the world of cloud computing. Microservices Journal offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. Follow new article posts on Twitter at @MicroservicesE
Mar. 28, 2015 12:00 PM EDT Reads: 1,353
Wearable technology was dominant at this year’s International Consumer Electronics Show (CES) , and MWC was no exception to this trend. New versions of favorites, such as the Samsung Gear (three new products were released: the Gear 2, the Gear 2 Neo and the Gear Fit), shared the limelight with new wearables like Pebble Time Steel (the new premium version of the company’s previously released smartwatch) and the LG Watch Urbane. The most dramatic difference at MWC was an emphasis on presenting wearables as fashion accessories and moving away from the original clunky technology associated with t...
Mar. 28, 2015 12:00 PM EDT Reads: 1,165
SYS-CON Events announced today the IoT Bootcamp – Jumpstart Your IoT Strategy, being held June 9–10, 2015, in conjunction with 16th Cloud Expo and Internet of @ThingsExpo at the Javits Center in New York City. This is your chance to jumpstart your IoT strategy. Combined with real-world scenarios and use cases, the IoT Bootcamp is not just based on presentations but includes hands-on demos and walkthroughs. We will introduce you to a variety of Do-It-Yourself IoT platforms including Arduino, Raspberry Pi, BeagleBone, Spark and Intel Edison. You will also get an overview of cloud technologies s...
Mar. 28, 2015 11:00 AM EDT Reads: 2,004
SYS-CON Events announced today that SafeLogic has been named “Bag Sponsor” of SYS-CON's 16th International Cloud Expo® New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. SafeLogic provides security products for applications in mobile and server/appliance environments. SafeLogic’s flagship product CryptoComply is a FIPS 140-2 validated cryptographic engine designed to secure data on servers, workstations, appliances, mobile devices, and in the Cloud.
Mar. 28, 2015 11:00 AM EDT Reads: 1,355
Containers and microservices have become topics of intense interest throughout the cloud developer and enterprise IT communities. Accordingly, attendees at the upcoming 16th Cloud Expo at the Javits Center in New York June 9-11 will find fresh new content in a new track called PaaS | Containers & Microservices Containers are not being considered for the first time by the cloud community, but a current era of re-consideration has pushed them to the top of the cloud agenda. With the launch of Docker's initial release in March of 2013, interest was revved up several notches. Then late last...
Mar. 28, 2015 09:15 AM EDT Reads: 2,158
SOA Software has changed its name to Akana. With roots in Web Services and SOA Governance, Akana has established itself as a leader in API Management and is expanding into cloud integration as an alternative to the traditional heavyweight enterprise service bus (ESB). The company recently announced that it achieved more than 90% year-over-year growth. As Akana, the company now addresses the evolution and diversification of SOA, unifying security, management, and DevOps across SOA, APIs, microservices, and more.
Mar. 28, 2015 08:30 AM EDT Reads: 1,999
After making a doctor’s appointment via your mobile device, you receive a calendar invite. The day of your appointment, you get a reminder with the doctor’s location and contact information. As you enter the doctor’s exam room, the medical team is equipped with the latest tablet containing your medical history – he or she makes real time updates to your medical file. At the end of your visit, you receive an electronic prescription to your preferred pharmacy and can schedule your next appointment.
Mar. 28, 2015 08:00 AM EDT Reads: 566
GENBAND has announced that SageNet is leveraging the Nuvia platform to deliver Unified Communications as a Service (UCaaS) to its large base of retail and enterprise customers. Nuvia’s cloud-based solution provides SageNet’s customers with a full suite of business communications and collaboration tools. Two large national SageNet retail customers have recently signed up to deploy the Nuvia platform and the company will continue to sell the service to new and existing customers. Nuvia’s capabilities include HD voice, video, multimedia messaging, mobility, conferencing, Web collaboration, deskt...
Mar. 28, 2015 01:00 AM EDT Reads: 1,400
The Open Compute Project is a collective effort by Facebook and a number of players in the datacenter industry to bring lessons learned from the social media giant's giant IT deployment to the rest of the world. Datacenters account for 3% of global electricity consumption – about the same as all of Switzerland or the Czech Republic -- according to people I met at the recent Open Compute Summit in San Jose. With increasing mobility at the edge of the cloud and vast new dataflows being predicted with the growth of the Internet of Things (and The Coming Age of Many Zettabytes) in the near...
Mar. 28, 2015 01:00 AM EDT Reads: 1,782
The list of ‘new paradigm’ technologies that now surrounds us appears to be at an all time high. From cloud computing and Big Data analytics to Bring Your Own Device (BYOD) and the Internet of Things (IoT), today we have to deal with what the industry likes to call ‘paradigm shifts’ at every level of IT. This is disruption; of course, we understand that – change is almost always disruptive.
Mar. 27, 2015 08:15 PM EDT Reads: 1,008
SYS-CON Events announced today that Cisco, the worldwide leader in IT that transforms how people connect, communicate and collaborate, has been named “Gold 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 City, NY. Cisco makes amazing things happen by connecting the unconnected. Cisco has shaped the future of the Internet by becoming the worldwide leader in transforming how people connect, communicate and collaborate. Cisco and our partners are building the platform for the Internet of Everything by connecting the...
Mar. 27, 2015 07:00 PM EDT Reads: 5,127
SYS-CON Media announced today that @WebRTCSummit Blog, the largest WebRTC resource in the world, has been launched. @WebRTCSummit Blog offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. @WebRTCSummit Blog can be bookmarked ▸ Here @WebRTCSummit conference site can be bookmarked ▸ Here
Mar. 27, 2015 06:00 PM EDT Reads: 1,678
Temasys has announced senior management additions to its team. Joining are David Holloway as Vice President of Commercial and Nadine Yap as Vice President of Product. Over the past 12 months Temasys has doubled in size as it adds new customers and expands the development of its Skylink platform. Skylink leads the charge to move WebRTC, traditionally seen as a desktop, browser based technology, to become a ubiquitous web communications technology on web and mobile, as well as Internet of Things compatible devices.
Mar. 27, 2015 06:00 PM EDT Reads: 1,721
SYS-CON Events announced today that robomq.io will exhibit at SYS-CON's @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. robomq.io is an interoperable and composable platform that connects any device to any application. It helps systems integrators and the solution providers build new and innovative products and service for industries requiring monitoring or intelligence from devices and sensors.
Mar. 27, 2015 06:00 PM EDT Reads: 1,355
Docker is an excellent platform for organizations interested in running microservices. It offers portability and consistency between development and production environments, quick provisioning times, and a simple way to isolate services. In his session at DevOps Summit at 16th Cloud Expo, Shannon Williams, co-founder of Rancher Labs, will walk through these and other benefits of using Docker to run microservices, and provide an overview of RancherOS, a minimalist distribution of Linux designed expressly to run Docker. He will also discuss Rancher, an orchestration and service discovery platf...
Mar. 27, 2015 04:15 PM EDT Reads: 2,367
Sonus Networks introduced the Sonus WebRTC Services Solution, a virtualized Web Real-Time Communications (WebRTC) offer, purpose-built for the Cloud. The WebRTC Services Solution provides signaling from WebRTC-to-WebRTC applications and interworking from WebRTC-to-Session Initiation Protocol (SIP), delivering advanced real-time communications capabilities on mobile applications and on websites, which are accessible via a browser.
Mar. 27, 2015 04:00 PM EDT Reads: 1,681
SYS-CON Events announced today that Aria Systems, the leading innovator in recurring revenue, has been named “Bronze Sponsor” of SYS-CON's @ThingsExpo, which will take place on June 9–11, 2015, at the Javits Center in New York, NY. Proven by the world’s most demanding enterprises, including AAA NCNU, Constant Contact, Falck, Hootsuite, Pitney Bowes, Telekom Denmark, and VMware, Aria helps enterprises grow their recurring revenue businesses. With Aria’s end-to-end active monetization platform, global brands can get to market faster with a wider variety of products and services, while maximizin...
Mar. 27, 2015 04:00 PM EDT Reads: 1,524
SYS-CON Events announced today that Vitria Technology, Inc. will exhibit at SYS-CON’s @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Vitria will showcase the company’s new IoT Analytics Platform through live demonstrations at booth #330. Vitria’s IoT Analytics Platform, fully integrated and powered by an operational intelligence engine, enables customers to rapidly build and operationalize advanced analytics to deliver timely business outcomes for use cases across the industrial, enterprise, and consumer segments.
Mar. 27, 2015 03:30 PM EDT Reads: 2,117