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SANS ISC: Analysis of a Distributed Denial of Service (DDoS) - SANS Internet Storm Center SANS ISC InfoSec Forums


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Analysis of a Distributed Denial of Service (DDoS)

I was sent this past week a file containing 10,711 unique IP addresses used in a DDoS. The entire DDoS occurred over a period of about 48 hours. This traffic is from the second day where all requests at the firewall were logged (1.5M reqs) and the traffic was dropped. Using the logs I was provided, I generated 3 graphs: a list of the TCP flags and the Top 10 ASN and countries associated with the source IPs.

The time frame of this activity occurred between 02:28 - 17:37 GMT. The first graph represents the TCP flags captured in this traffic. The data contains over 1.5M SYN packets followed by just over eighteen thousand TCP RST packets, etc. This is not a huge DDoS since it occurred over a period of 15 hours, it amounts to about 104,300 packets per hour.

TCP Flags

I used Maxmind geoiplookup[1] tool to graph only the top 10 Autonomous System Number (ASN) and countries assigned to each inbound IPs. Since it is a DDoS, I have to assume the traffic is likely spoofed and likely controlled by a botnet.

Maxmind Analysis of IPs by ASN - Top 10

Maxmind Analysis of IPs by Countries - Top 10

Just for fun, I also sorted the TCP options. Below is the Top 20 list. What is also interesting in this output is the most common windows of 8192 which is usually associated with the Windows OS. The maximum segment size (MSS) is anywhere between 1360 to 1460 use to indicate the maximum payload a packet can carry which might be associated with smaller MTU. For example, an MTU of 1452 is often associated with PPPoE and DSL routers.[4] The 16,628 packets with a "win 0, length 0" are all the Reset packets captured in the traffic.

Count                    TCP Options

 131661  win 8192, options [mss 1460,nop,wscale 2,nop,nop,sackOK], length 0
 115274  win 8192, options [mss 1460,nop,nop,sackOK], length 0
  69531  win 8192, options [mss 1452,nop,nop,sackOK], length 0
  66714  win 65535, options [mss 1460,nop,nop,sackOK], length 0
  66670  win 8192, options [mss 1452,nop,wscale 2,nop,nop,sackOK], length 0
  61611  win 8192, options [mss 1460,nop,wscale 8,nop,nop,sackOK], length 0
  43965  win 8192, options [mss 1452,nop,wscale 8,nop,nop,sackOK], length 0
  35975  win 65535, options [mss 1452,nop,nop,sackOK], length 0
  31301  win 8192, options [mss 1412,nop,wscale 2,nop,nop,sackOK], length 0
  25286  win 8192, options [mss 1412,nop,nop,sackOK], length 0
  19160  win 8192, options [mss 1400,nop,nop,sackOK], length 0
  18457  win 8192, options [mss 1440,nop,nop,sackOK], length 0
  18290  win 8192, options [mss 1440,nop,wscale 2,nop,nop,sackOK], length 0
  17903  win 8192, options [mss 1440,nop,wscale 8,nop,nop,sackOK], length 0
  17418  win 8192, options [mss 1360,nop,wscale 2,nop,nop,sackOK], length 0
  16628  win 0, length 0
  15921  win 8192, options [mss 1400,nop,wscale 8,nop,nop,sackOK], length 0
  15058  win 8192, options [mss 1360,nop,nop,sackOK], length 0
  14720  win 8192, options [mss 1400,nop,wscale 2,nop,nop,sackOK], length 0
  14651  win 8192, options [mss 1380,nop,wscale 2,nop,nop,sackOK], length 0

[1] https://github.com/maxmind/geoip-api-c
[2] http://kbeezie.com/geoiplookup-command-line/
[3] https://isc.sans.edu/forums/diary/DDOS+is+down+but+still+a+concern+for+ISPs/20701
[4] http://www.cisco.com/c/en/us/support/docs/long-reach-ethernet-lre-digital-subscriber-line-xdsl/asymmetric-digital-subscriber-line-adsl/12918-router-mtu.html
[5] http://dev.maxmind.com/geoip/legacy/geolite/
[6] https://en.wikipedia.org/wiki/Autonomous_system_%28Internet%29

 

-----------
Guy Bruneau IPSS Inc.
Twitter: GuyBruneau
gbruneau at isc dot sans dot edu

Guy

418 Posts
ISC Handler
Guy,

Great analysis- it is so interesting to see the story told by the data and is so much more valuable than "we just had a DDoS".

Russell
Russell

90 Posts Posts
ISC Handler
Thanks Russell. Yes putting context around the traffic usually help visualize the data to provide a clearer picture of the activity.
Guy

418 Posts Posts
ISC Handler
hi,

couldnt you get more out of the data like rps/time, volume/time etc?


cheers, mex
Anonymous
Posts
Hi Guy,
First great analysis! always interesting to learn more about the subject of DDoS.
But except for the need pursue knowledge, do you think such data can help organizations deal with DDoS attacks? If so how?
Anonymous
Posts
Hi Mex, Unfortunately, that is all I could extract from the data.
Guy

418 Posts Posts
ISC Handler
DDoS attack are always difficult to deal with. Sometimes the most effective way to deal with this is to have a good relationship with your ISP to see if they can help block the traffic. You could also try to block the traffic yourself but that might also exhaust your bandwidth or limit access to your resources.
Guy

418 Posts Posts
ISC Handler

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