Network Based Application Recognition

Network Based Application Recognition (NBAR)[1] is the mechanism used by some Cisco routers and switches to recognize a dataflow by inspecting some packets sent.

The networking equipment which uses NBAR does a deep packet inspection on some of the packets in a dataflow, to determine which traffic category the flow belongs to. Used in conjunction with other features, it may then program the internal application-specific integrated circuits (ASICs) to handle this flow appropriately. The categorization may be done with Open Systems Interconnection (OSI) layer 4 info, packet content, signaling, and so on but some new applications have made it difficult on purpose to cling to this kind of tagging.[2]

The NBAR approach is useful in dealing with malicious software using known ports to fake being "priority traffic", as well as non-standard applications using dynamic ports.[3] That's why NBAR is also known as OSI layer 7 categorization.

On Cisco routers, NBAR is mainly used for Quality of Service and Security purposes.

References
  1. NBAR defined at Cisco website
  2. BitTorrent Encryption and Obfuscation
  3. Using Network-Based Application Recognition and ACLs for Blocking the "Code Red" Worm, Cisco.


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