Is there any way to monitor DoS attacks with SNMP or any other software which based on Linux and could monitor router / switches and alert when a DoS attack is observed?
closed as not a real question by pauska, Scott Pack, EEAA, HopelessN00b, Ladadadada Aug 27 '12 at 13:21
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There most certainly is, though it depends on the nature of the DoS and the instrumentation exposed by SNMP.
Be sure to set above-normal alert threshold in your monitoring package, and you should catch those.
SNMP is only a tool to retrieve informations, counters, from a device.
Using only snmp, you'll only be able to get traffic flowing through the interfaces, and basic informations such as CPU and RAM usage.
Netflow, on the other hand, is a protocol designed to report flow pattern, and is very useful to detect DoS attacks.
You can combine the two and use a Netflow MIB that will report the top-talkers, and allow you to monitor the ongoing DoS.