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The new Alter-Any-Field Impairment provides a mechanism to drill down and precisely replicate a specific fuzz test failure condition for less than half the price of a high end fuzz tester, for highly cost-effective protocol testing.

SCOTTS VALLEY, Calif.  (May 12, 2011) -- InterWorking Labs, developers of network emulators and protocol testers to improve the quality and operation of voice, video, and data networks, today announced the Alter-Any-Field Impairment.

With a few simple clicks from the graphical user interface, an engineer can modify incoming packets that meet specified criteria. The engineer can change any field or fields in any network packet, in real time, while the network conversation is occurring.

The Maxwell Alter-Any-Field Impairment could be extremely useful in:

  • Replicating a specific fuzz test to verify the robustness of a device
  • Debugging complex problems where the engineer has packet captures but not the original device (a form of capture and replay)
  • Creating a new set of tests for a particular feature, without learning a programming language.


During the network conversation the Alter-Any-Field Impairment can:

  • Insert or append bytes (padding) into a protocol packet's payload or header
  • Remove bytes from a protocol packet's payload or header
  • Find and remove specific IPv4, IPv6, or TCP options (enabling IPv6 tests)
  • Rewrite any header field or payload bytes, such as source or destination IP addresses
  • Automatically update protocol length fields after byte insertions and deletions
  • Perform operations on byte strings inside the packet, such as addition, bit-wise "and", "or", and "xor"
  • Recompute all checksums upon the engineer's request
  • Perform the alterations to a copy of the original packet and send the altered copy before or after the original packet - thus allowing insertion of entirely new packets into the network dialog


The Alter-Any-Field Impairment even understands tunneling - so, for example, a request to modify the first IPv6 datagram header will be performed even when that IPv6 datagram is tunneled inside an IPv4 datagram.

Once an engineer has defined one or more Alter-Any-Field impairments, they may be saved and replayed at a future time.

The Alter-Any-Field Impairment may also be combined with other standard impairments such as jitter, delay, re-ordering, etc.

Compared with other commercial and open source tools, the Alter-Any-Field Impairment :

  • Lets the engineer modify a live packet from a real-world network conversation; no need to create a new packet from scratch.
  • Supports "man in the middle" operation by sitting between two devices, intercepting the network traffic; it is not limited to creating a packet that is sent to an end point.
  • Alters multiple, concurrent packets; operation is not limited to one packet at a time.
  • Operates via a point and click graphical interface; there is no requirement to learn a special programming language built on top of another programming language.
  • Keeps up with the flow of traffic for accurate emulation; does not slow down and burden network operation.


The Alter-Any-Field Impairment is available NOW and shipping with the Maxwell Network Emulator. To learn more and see it in action, sign up for our next webinar.

With Alter-Any-Field, an engineer can modify incoming packets that meet specified criteria via a graphical interface. The engineer can change any field or fields in any network packet, in real time, while the network conversation is occurring. Alter-Any-Field is available with the Maxwell Network Emulator from InterWorking Labs.