The majority of the source is covered by:

Copyright (c) 1995 The Regents of the University of California.
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.
3. Neither the name of the University nor of the Laboratory may be used
   to endorse or promote products derived from this software without
   specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.

Note that BSD license from University of California has degreed that clause 3
be deleted as per;
ftp://ftp.cs.berkeley.edu/pub/4bsd/README.Impt.License.Change
However alot of the existing still has the old style license.

For information clause 3:
3. All advertising materials mentioning features or use of this software
   must display the following acknowledgement:
     This product includes software developed by the Network Research
     Group at Lawrence Berkeley National Laboratory.


The remainder of the source code is covered by: 
BSD style licence from University College London. Other source files are under a new-BSD licence from external institutions including Stichting Mathematisch Centrum, Amsterdam, Sun Microsystems Inc, Xerox Corporation, Apple Computer Inc, University of British Columbia, and WIDE Project. Others files are under the old-BSD license from Argonne National Laboratory/University of Chicago. Some files are freely licensed by the Internet Software Consortium. 

In addition to the license holders above there copyright holders including; Bell Communications Research, RSA Data Security, Inc. Nortel Networks, University of Sydney, Technische Universitaet Berlin, British Telecommunications Plc, Brook Milligan, Intel Corporation, HEWLETT-PACKARD COMPANY, Luigi Rizzo, University of Sydney Vislab, Software Research Associates, Inc, Telenor Research and Development.

