Packet loss Detection and Recovery

The Internet is not a safe place. Unsecured hosts can expect to be compromised within minutes of connecting to the Internet and even well-protected hosts may be crippled with denial-of-service (DoS) attacks. We consider the problem of detecting whether a compromised router is maliciously manipulating its stream of packets. In particular, we are concerned with a simple yet effective attack in which a router selectively drops packets destined for some Victim. Unfortunately, it is quite challenging to attribute a missing packet to a malicious action because normal network congestion can produce the same effect. Modern networks routinely drop packets when the load emporarily exceeds their buffering capacities. Previous detection protocols have tried to address this problem with a user-defined threshold: too many dropped packets imply malicious intent. However, this heuristic is fundamentally unsound; setting this threshold is, at best, an art and will certainly create unnecessary false positives or mask highly focused attacks.

Random early detection (RED), also known as random early discard or random early drop is an active queue management algorithm. It is also a congestion avoidance algorithm. In the conventional tail drop algorithm, a router or other network component buffers as many packets as it can, and simply drops the ones it cannot buffer. If buffers are constantly full, the network is congested. Tail drop distributes buffer space unfairly among traffic flows. Tail drop can also lead to TCP global synchronization as all TCP connections "hold back" simultaneously, and then step forward simultaneously. Networks become under-utilized and flooded by turns. RED addresses these issues.

RED monitors the average queue size, based on an exponential weighted moving average: where the actual queue size and weight for a low-pass filter. RED uses three more parameters in minimum threshold,
Maximum, Maximum threshold. Using, RED dynamically computes a dropping probability in two steps for each packet it receives. First, it computes an interim probability, Further; the RED algorithm tracks the number of packets, since the last dropped packet. The final dropping probability, p, is specified to increase slowly as increases.

Network routers occupy a unique role in modern distributed systems. They are responsible for cooperatively shuttling packets amongst themselves in order to provide the illusion of a network with universal point-to-point connectivity. However, this illusion is shattered - as are implicit assumptions of availability, confidentiality, or integrity - when network routers are subverted to act in a malicious fashion. By manipulating, diverting, or dropping packets arriving at a compromised router, an attacker can trivially mount denial-of-service, surveillance, or man-in-the-middle attacks on end host systems. Consequently, Internet routers have become a choice target for would-be attackers and thousands have been subverted to these ends. In this paper, we specify this problem of detecting routers with incorrect packet forwarding behavior and we explore the design space of protocols that implement such a detector. We further present a concrete protocol that is likely inexpensive enough for practical implementation at scale. Finally, we present a prototype system, called Fatih, that implements this approach on a PC router and describe our experiences with it. We show that Fatih is able to detect and isolate a range of malicious router actions with acceptable overhead and complexity. We believe our work is an important step in being able to tolerate attacks on key network infrastructure components.

We have designed, developed, and implemented a compromised router detection protocol that dynamically infers, based on measured traffic rates and buffer sizes, the number of congestive packet losses that will occur.

Once the ambiguity from congestion is removed, subsequent packet losses can be attributed to malicious actions. We have tested our protocol in Emulab and have studied its effectiveness in differentiating attacks from legitimate network behavior.


Step 1: Start the process
Step 2: Trace the incoming packets using Jpcap (Java Component used to capture the packets)
Step 3: Assign scores to the packets based on the Log Conditional Legitimate Probability (CLP)
Step 4 : Fix the threshold value which depends on the parameters like protocol type, packet size etc.,
Step 5: Compare the Threshold value with the Packet Score
Step 6: If the Measured value is less than the Threshold value then the packet is attacked packet Other wise, the packet is normal packet
Step 7: Update the cumulative distribution function score and continue with the Step 3.
Step 8: Stop the process

To the best of our knowledge, this paper is the first serious attempt to distinguish between a router dropping packets maliciously and a router dropping packets due to congestion.
Previous work has approached this issue using a static user-defined threshold, which is fundamentally limiting. Using the same framework as our earlier work (which is based on a static user-defined threshold) we developed a compromised router detection protocol _ that dynamically infers, based on measured traffic rates and buffer sizes, the number of congestive packet losses that will occur.
Subsequent packet losses can be attributed to malicious actions. Because of non determinism introduced by imperfectly synchronized clocks and scheduling delays, protocol _ uses user-defined significance levels, but these levels are independent of the properties of the traffic. Hence, protocol _ does not suffer from the limitations of static thresholds. We evaluated the effectiveness of protocol _ through an implementation and deployment in a small network. We show that even fine-grained attacks, such as stopping a host from opening a connection by discarding the SYN packet, can be detected.

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