CCNP Recertification

Posted on Monday, 29th December 2008 by sean

The last article used flow-nfilter and some variable substitution to pull out all flows to a particular address. The next useful thing would be to pull out all flows to or from a particular network. To do so, we’ll have to define a new primitive that is a variable network/netmask, and then a filter specifying [...]

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Posted on Tuesday, 23rd December 2008 by sean

Yesterday, we had a web site crash. I was curious if it had to do with load or something else was going on. This is a great opportunity to show how to analyze NetFlow data. First, I should mention that there may be easier ways of doing this. The flow-tools package includes a lot of [...]

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Posted on Monday, 22nd December 2008 by sean

In the NetFlow world, a NetFlow exporter sends flow data to a NetFlow collector. The exporter is usually a router, the collector is usually a Unix server of some sort. First, set up your router to export flow information: ip flow-cache timeout active 2 mls flow ip full mls flow ipx destination mls nde sender [...]

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Posted on Saturday, 20th December 2008 by sean

NetFlow is a technology that lets a router export information about current traffic to a collector for analysis. The analysis might be real time, such as to detect a denial of service attack, or not real time, such as to view trending information. NetFlow is concerned with flows, which are a one way session between [...]

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