What's "dropping source port zero packet", attack ?

[C.S.Chen]

Hi, 

What's the meaning of the following messages ?

s/w: BIND 8.2.2-P5.
---------------------------------------------------------------------
09-Dec-1999 09:22:36.190 notice: dropping source port zero packet from [63.224.10.78].0
08-Dec-1999 17:30:07.256 notice: dropping source port zero packet from [63.224.10.78].0 08-Dec-1999 17:30:43.263 notice: dropping source port zero packet 
from [63.224.10.78].0
08-Dec-1999 06:36:18.818 notice: dropping source port zero packet from [207.91.15.26].0
08-Dec-1999 06:36:20.820 notice: dropping source port zero packet from [207.91.15.26].0
08-Dec-1999 06:36:23.837 notice: dropping source port zero packet from [207.91.15.26].0
---------------------------------------------------------------------
Some DoS attack ?

Here is the related part from the BIND source code, 

ns_main.c
==============
 /* Drop UDP packets from port zero.  They are invariable forged. */
        if (qsp == NULL && ntohs(from.sin_port) == 0) {
                ns_notice(ns_log_security,
                          "dropping source port zero packet from %s",
                          sin_ntoa(from));
                return;
        }                                


-- 
Joe. C.S.Chen, cschen at nctu.edu.tw
* Computer Center of National Chiao Tung University, Hsinchu, Taiwan.