faq

A Java wrapper for WinPcap. It allows Java code to access to the WinPcap on win32.

$Id: FAQ,v 1.13 2004/04/06 22:14:38 pcharles Exp $

                             jpcap FAQ


General

  Q. Can I use JDK1.3, J2SE 1.4 or J2SE 1.5?

  A. Yes. Jpcap has been tested with these VM's and works fine.
     For backward compatibility, though, it doesn't yet utilize any 
     VM features specific to J2SE 1.3 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 or better
     is highly recommended. In general, the performance of the 1.3 VM 
     is superior to 1.2. The difference is especially noticeable in jpcap 
     when using the graphical component of 
     net.sourceforge.jpcap.client.CaptureTool to visualize network traffic. 


  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 trying to create multiple PacketCapture instances, and 
     it isn't working properly.

  A. Upgrade to jpcap v0.01.15 or later. Multiple simultaneous 
     packet capture instances within the same Java VM weren't supported 
     in earlier versions of jpcap.


  Q. I'm trying to run jpcap, or an application written to use the packet
     capture library, and I'm getting an error similar to:

       loading native library jpcap.. Exception in thread "main" 
       java.lang.UnsatisfiedLinkError: no jpcap in java.library.path

  A. This means that the jpcap shared library is not in your path.
     On Windows, this means that jpcap.dll is not one of the directories 
     specified by the PATH environment variable. On Unix, this means that 
     the file libjpcap.so is not in one of the directories specified by your 
     LD_LIBRARY_PATH. On Mac OS X, this means that the file libjpcap.jnilib
     is not in one of the directories specified by your 
     DYLD_LIBRARY_PATH.


Linux 

  Q. When trying to install the jpcap rpm, I get the message:
       error: Failed dependencies:
         libstdc++-libc6.2-2.so.3 is needed by jpcap-0.01.16-1

  A. Install the compat-stdc++ rpm for backward compatibility.
       e.g. 'yum install compat-libstdc++'


  Q. When trying to run jpcap, I get the following error:
       /usr/java/j2sdkx.y/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.
       e.g. 'yum install compat-libstdc++'


  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. 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. 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.


  Q. How do I build jpcap on my Linux box?

  A. See the document 'docs/BUILD.unix' in the source distribution.


Mac OS X

  Q. How do I build jpcap on my Mac OS X?

  A. See the document 'docs/BUILD.osx'.


  Q. When I run the jpcap sample client, I can capture packets, but when I 
     try to manipulate the vectors in visualization window, it freezes.

  A. This appears to be a bug specifically in the Java implementation for 
     Mac OS X. No known workarounds exist, but submissions (perhaps from 
     someone more intimiately familiar with Mac OS X Java internals?) would 
     be very welcome.:/


  Q. I can't get jpcap to build from source on my Mac.

  A. Upgrade to jpcap v0.01.14 or later. The makefiles in earlier versions 
     of jpcap didn't support the Mac OS X platform without modification.
     If you are already using jpcap v0.01.14 and still having problems, 
     try looking at the document 'docs/BUILD.osx'.


Windows 

  Q. How do I build jpcap on my Windows box?

  A. See the document 'docs/BUILD.windows'.


  Q. When I run the jpcap.bat file on Windows, I can capture and display 
     packets, but the console text is cluttered by weird characters.
     These strange characters are really scaring me; they look like this:
       [<-[1;33mTCPPacket<-[0m:

  A. These strange characters are ansi escape sequences which, on most 
     platforms, cause the text (in this case 'TCPPacket') to appear 
     in different colors. These ansii escape sequences don't work in DOS.
     They can be disabled in properties/tool.properties by changing 
       net.sourceforge.jpcap.console.color=false