GBF: a grammar based filter for internet applications
Journal of Network and Computer Applications
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The Universal Packet Analyzer is a Unix user program that filters a network packet and reports its contents. The term "Universal" is used to indicate that this program is not limited to a particular protocol stack nor is it limited by the number of layers. The software has an intuitive window-based graphical interface and is mouse driven. The input is a Hex packet stream read from user designated files and the output is the filtered packet, which can be viewed either online or offline. The code is written in ''C'' and the graphical user interface was built using devguide, the OpenWindows Software Developer''s Guide. Packets are defined with the aid of a simple scripting language called the Packet Definition Language (PDL) [1] and [2]. The PDL has constructs that support the layered architecture concept of networks. The user can inspect the packet at any layer using filters. Filters are built up from filter clauses, written in a simple scripting language called the Filter Definition Language (FDL) [1] and [2]. The package has a number of supplementary services that support the main activity of filtering packets. The user has the capability of saving and naming the current configuration of packet definitions and filters. The user can return to this configuration by name, thus saving time. The user can build and edit both filters and packet definitions on the fly.