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Intention-Driven iTrace

Intention-Driven iTrace. S. Felix “ Last Minutes ” Wu UC Davis http://www.cs.ucdavis.edu/~wu wu@cs.ucdavis.edu Lixia Zhang UCLA Allison Mankin, Dan Massey USC/ISI. A Statistic Problem with iTrace.

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Intention-Driven iTrace

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  1. Intention-Driven iTrace S. Felix “Last Minutes” Wu UC Davis http://www.cs.ucdavis.edu/~wu wu@cs.ucdavis.edu Lixia Zhang UCLA Allison Mankin, Dan Massey USC/ISI ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  2. A Statistic Problem with iTrace • Routers closer to the victims have higher probability to generate iTrace packets toward the true victims. • Routers closer to the DDoS slaves might have relatively small probability (smaller than the routers around the victims) to generate “useful” iTrace packets. ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  3. Two measures • P(U-iTrace) • When an iTrace message is generated, what is the probability that this iTrace message is “useful” (i.e., it carries an attack packet)? • P(U-iT-sec) • What is probability for a router to generate at least ONE “useful” iTrace message in a second? ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  4. Slave R1 R2 Victim Example: Multi-S Single-V 1K attack-pkt/sec 19K normal-pkt/sec P(U-iTrace) = 5% #iTrace/sec = 1 P(U-iT-sec) = 5% 200K attack-pkt/sec 200K normal-pkt/sec P(U-iTrace) = 50% #iTrace/sec = 20 P(U-iT-sec) = 99.999% 4K attack-pkt/sec 196K normal-pkt/sec P(U-iTrace) = 2% #iTrace/sec = 10 P(U-iT-sec) = 18% 980K attack-pkt/sec 20K normal-pkt/sec P(U-iTrace) = 98% #iTrace/sec = 50 P(U-iT-sec) = 100% ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  5. Motivation • About (K* 0.005%) of our network resources will be spent on iTrace packets. • Then, we hope we can spend the resources on more “useful” iTrace packets. ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  6. Three Types of Nodes • DDoS victim with the intention to trace the slaves. • DDoS victim without the intention. • non-DDoS victims (assuming they do not have the intention as well -- and very likely they hope they won’t receive ones). ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  7. Intention-driven iTrace • Different destinationhosts, networks, domains/ASs have different “intention levels” in receiving iTrace packets. • We propose to add one “iTrace-intention” bit. • Some of them might not care about iTrace, and some of them might not be under DDoS attacks, for example. ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  8. a little mathematics... Intention for receiving iTrace. S2V: 2% I: 1 S2B:48% I: 0 S2C:25% I: 0 S2D:25% I: 1 V’s probability to receive iTrace packets: 7.41% 0.02 / (0.02 + 0 + 0 + 0.25) = 0.0741 PiTrace(V) = (Ptraffic(V) * I(V)) / (Ptraffic(n) * I(n)) ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  9. Slave R1 R2 Victim Example: Multi-S Two-V 4K att-v1-pkt/sec 50K att-v2-pkt/sec 146K normal-pkt/sec P(U-iTrace) = 2% #iTrace/sec = 10 P(U-iT-sec) = 18% I(Victim-1) = 1 P(U-iTrace) = 7.4% P(U-iT-sec) = 53.7% P(U-iTrace) = 25% #iTrace/sec = 10 P(U-iT-sec) = 95% I(Victim-2) = 1 P(U-iTrace) = 92.6% P(U-iT-sec) = 100.0% ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  10. Issues • How to determine the intention bit? • Policy to set the bit. • How to distribute the intention bits to routers globally? • Utilize/extend BGP! • How to use the intention bits at each router? ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  11. How to distribute I(n)? • YABE: (Yet Another BGP Extension) • For every BGP route update, we include I(n) as a new community attribute: • 0x[iTrace-Intention]:0x[0-1] • These I(n) values will be forwarded or even aggregated by the routers who understand this new community attribute. • aggregation: I(new) = max {I(n)} • Rate-Limiting on Intention Update: • should not be more frequent than Keep-Alive messages. • should not trigger any major route computation. ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  12. The iTrace Statistics Model Packet buffering Routing table lookup Forward process Should this packet be iTraced? iTrace Stochastic Process Yes, we should generate an iTrace for this packet? ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  13. iTrace Trigger Packet buffering Routing table lookup Forward process iTrace Trigger If yes, pick the Nth packet in the buffer…. iTrace Stochastic Process Should we generate an iTrace message now? ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  14. A simple design iTrace Process BGP table I(n) iTrace bit per ~20K pkts Add two bits to the routing table: (1). I(n): Intention Bit Value associated with this entry (2). iTrace bit: whether we need to generate an iTrace message for this entry now. ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  15. Handling an iTrace Trigger iTrace Process • If all I(n)’s are zero, shut-off the iTrace trigger process. • Set the iTrace bit on all the entries with I(n) = 1. BGP table I(n) iTrace bit ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  16. (1). Before iTrace trigger: 152.1.23.0/24 1 0 169.20.3.0/24 0 0 192.1.0.0/16 0 0 207.3.4.183/20 1 0 152.1.0.0/16 1 0 155.0.0.0/16 0 0 (2). After iTrace trigger: 152.1.23.0/24 1 1 169.20.3.0/24 0 0 192.1.0.0/16 0 0 207.3.4.183/20 1 1 152.1.0.0/16 1 1 155.0.0.0/16 0 0 ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  17. (3). After iTrace sent: 152.1.23.0/24 1 0 169.20.3.0/24 0 0 192.1.0.0/16 0 0 207.3.4.183/20 1 0 152.1.0.0/16 1 0 155.0.0.0/16 0 0 ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  18. Processing Overhead 1/20K iTrace message trigger occurs: 1. Set all the iTrace bits on if I(n) = 1. Processing for each data packet: 1. if the iTrace flag bit is 1, (1). send an iTrace message for this data packet. (2). reset all the iTrace bits to 0. ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  19. Slave R1 R2 Victim The Aggregation Problem 4K att-v1-pkt/sec 50K att-v2-pkt/sec 146K normal-pkt/sec P(U-iTrace) = 2% #iTrace/sec = 10 P(U-iT-sec) = 18% I(Victim-1) = 1 P(U-iTrace) = 7.4% for 4K traffic. P(U-iT-sec) = 53.7% 4K att-v1-pkt/sec 16K agg-v1-pkt/sec 50K att-v2-pkt/sec 130K normal-pkt/sec P(U-iTrace) = 2% #iTrace/sec = 10 P(U-iT-sec) = 18% I(Victim-1) = 1 P(U-iTrace) = 5.7% for 20K traffic. P(U-iT-sec) = 44.4% ICMP Traceback Working Group, IETF'50, Minneapolis, MN

  20. Summary for Intention iTrace • Improve the probability of “useful” iTrace. • Require some “minor” changes to the router forwarding process. • Require another BGP extension. • We need to verify that this extension will be interoperable well with existing BGP nodes. • The amount of generated iTrace messages should be no more than the current iTrace proposal. ICMP Traceback Working Group, IETF'50, Minneapolis, MN

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