The best way we use to identify DOS attacks is measuring and monitoring the backbone circuits the packets/second in and out, normally most of the DOS attacks generated a lot of packets/second, in our case we created an alarm that sends an email and page each time any of our backbone circuits exceed 17000 Packets/second, second alarm when packets exceed 20k using Intermapper 3.6 and SNMP.
After this is you are using the Cisco 12000 is no problem to try of detect the type of traffic using Extended Access-list and sending to the loggin for 15-20 seconds and then look for ICMP, UDP and TCP, in our case we found 7 of ten DOS attacks target IP's and only 10% are coming from known sources, most of the attacks used smurfed sources.
Antonio J. Pena
Senior Manager, Network Engineering
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