Dell PowerConnect B-RX BigIron RX Series Configuration Guide v02.8.00 - Page 1071

Chapter Protecting Against Denial of Service Attacks 34 In a Denial of Service (DoS) attack, a router is flooded with useless packets, hindering normal operation. The BigIron RX includes measures for defending against two types of DoS attacks, Smurf attacks and TCP SYN attacks. Protecting against Smurf attacks A Smurf attack is a kind of DoS attack where an attacker causes a victim to be flooded with ICMP echo (Ping) replies sent from another network. Figure 132 illustrates how a Smurf attack works. FIGURE 132 How a Smurf attack floods a victim with ICMP replies 1 Attacker sends ICMP echo requests to broadcast address on Intermediary's network, spoofing Victim's IP address as the source Attacker 2 If Intermediary has directed broadcast forwarding enabled, ICPM echo requests are broadcast to hosts on Intermediary's network Intermediary 3 The hosts on Intermediary's network send replies to Victim, inundating Victim with ICPM packets Victim The attacker sends an ICMP echo request packet to the broadcast address of an intermediary network. The ICMP echo request packet contains the spoofed address of a victim network as its source. When the ICMP echo request reaches the intermediary network, it is converted to a Layer 2 broadcast and sent to the hosts on the intermediary network. The hosts on the intermediary network then send ICMP replies to the victim network. For each ICMP echo request packet sent by the attacker, a number of ICMP replies equal to the number of hosts on the intermediary network are sent to the victim. If the attacker generates a large volume of ICMP echo request packets, and the intermediary network contains a large number of hosts, the victim can be overwhelmed with ICMP replies. BigIron RX Series Configuration Guide 995 53-1002253-01