$Id: FAQ,v 1.5 2002/07/16 16:34:28 pcharles Exp $

                             jpcap FAQ


  Q. Can I use JDK1.1?

  A. No. jpcap uses the new JNI (Java Native Interface) and 
     new collection classes which are not available in or compatible 
     with JDK1.1. You need to use J2SE, JDK1.2 or later.


  Q. I'm using JDK1.2 and the performance is terrible.

  A. Although the project compiles and runs under JDK1.2, JDK1.3.1 is 
     highly recommended. (1.3.0_02 is ok, but isn't very stable on Linux.) 
     In general, the performance of the 1.3 VM is superior to 1.2.
     The difference is especially noticable in jpcap when using 
     the graphical component of net.sourceforge.jpcap.client.CaptureTool
     to visualize network traffic. 


  Q. Can I use JDK1.4?

  A. Yes. Jpcap has been tested with JDK1.4 and works fine.
     For backward compatibility, though, it doesn't yet utilize any 
     VM features specific to 1.4.


  Q. I'm trying to use jpcap on my Alpha AXP machine, but I can't 
     capture any packets.

  A. There are problems with older versions of libpcap on Alpha.
     On 2.2.5-22 kernel Alpha machine, libpcap-0.4-19 and
     libpcap-0.4-29 distributions packaged by redhat do not work.
     All pcap functions return normally, but after entering 
     pcap_loop(), no packets are ever captured and the handler
     never called back.

     On alpha, upgrade to the latest version of libpcap.
     libpcap-0.6.2-3 (included in RawHide for Alpha distro) 
     is recommended. Try rpmfind.org to locate the latest for 
     your distribution.


  Q. I'm calling PacketCapture.getNetwork() and .getNetmask(), and 
     the methods always return zero or garbage.

  A. These functions return random values which change with every 
     invocation on some older versions of libpcap, notably 0.4-16 
     included with the tool ethereal.

     Upgrading to libpcap v0.6.2 or later is recommended.


  Q. When trying to run jpcap, I get the following error:
     /usr/java/jdk1.3.1/bin/i386/native_threads/java: 
     error while loading shared libraries: libstdc++-libc6.1-1.so.2: 
     cannot open shared object file: No such file or directory

  A. Install the libstdc++ backward compatibility RPM:
     compat-libstdc++-6.2-2.9.0.16.i386.rpm


  Q. When trying to run jpcap, I get the following error:
     "too many registers needed to evaluate expression".

  A. This is a bug in libpcap. Upgrade to a version later than 
     0.7, or if you are compiling your own libpcap, look for 
     Ken Key's patch to gencode.c which fixes the problem.


