1. 1 Controlling High Bandwidth Aggregates in the Network

2. 2 Goals: Handle congestion Limit DoS attacks Allow flash crowds Identify traffic aggregates Subset of flows responsible for congestion Integrate provider policy Allow provider to configure drop mechanism

3. 3 Related Work IP Traceback Tries to find source of attack Ingress/Egress Filtering ISP filters packets with fake source addresses Input debugging Uses signatures to filter attack traffic Scheduling: Fair Queuing Deficit Round Robin

4. 4 ACC Design Apply congestion control to aggregated traffic Two levels of control: Local:  Identification  Control Global:  Pushback*

5. 5 Issues Collateral damage Legitimate traffic may be inaccurately identified and restricted Routers may become synchronized and simultaneously detect congestion Insert jitter into monitoring interval How to ensure fairness of flows Separate identification and control Use RED to manage queue drops

6. 6 Application to DoS attacks: Finding Aggregates Match destination of each dropped IP packet with longest matching prefix in routing table Periodically find most frequent prefix See if destinations match longer prefix E.g. maybe all dropped packets go to some specific host.

7. 7 Application to DoS attacks: Rate Limiting* Let: w o be output bandwidth w i be total input bandwidth w b be bandwidth of aggregate desired drop rate be 20% Two conditions: w i – w b <= 1.2*w o w i – w b > 1.2*w o