今天在打开c:\windows\pfirewall.log文件时，发现很多这样的行，如下：
2011-04-20 08:37:43 DROP UDP 192.168.1.212
239.255.255.250 1042 1900 161 – – – – – – – RECEIVE
2011-04-20 08:37:46 DROP
UDP 192.168.1.212 239.255.255.250 1042 1900 161 – – – – – – –
RECEIVE
2011-04-20 08:37:49 DROP UDP 192.168.1.212 239.255.255.250 1042 1900
161 – – – – – – – RECEIVE
2011-04-20 08:41:20 DROP UDP 192.168.1.50
239.255.255.250 1048 1900 160 – – – – – – – RECEIVE
2011-04-20 08:41:20 DROP
UDP 192.168.1.50 239.255.255.250 1048 1900 160 – – – – – – –
RECEIVE
2011-04-20 08:41:20 DROP UDP 192.168.1.50 239.255.255.250 1048 1900
160 – – – – – – – RECEIVE
2011-04-20 08:41:20 DROP UDP 192.168.1.50
239.255.255.250 1048 1900 160 – – – – – – – RECEIVE
2011-04-20 08:41:20 DROP
UDP 192.168.1.50 239.255.255.250 1048 1900 160 – – – – – – –
RECEIVE
2011-04-20 08:41:20 DROP UDP 192.168.1.50 239.255.255.250 1048 1900
161 – – – – – – – RECEIVE
2011-04-20 08:41:20 DROP UDP 192.168.1.50
239.255.255.250 1048 1900 161 – – – – – – – RECEIVE
2011-04-20 08:41:20 DROP
UDP 192.168.1.50 239.255.255.250 1048 1900 161 – – – – – – –
RECEIVE
2011-04-20 08:41:20 DROP UDP 192.168.1.50 239.255.255.250 1048 1900
161 – – – – – – – RECEIVE
2011-04-20 08:41:20 DROP UDP 192.168.1.50
239.255.255.250 1048 1900 161 – – – – – – – RECEIVE
2011-04-20 08:42:37 DROP
UDP 192.168.1.189 239.255.255.250 1037 1900 161 – – – – – – –
RECEIVE
2011-04-20 08:42:34 DROP UDP 192.168.1.189 239.255.255.250 1037 1900
161 – – – – – – – RECEIVE
2011-04-20 08:42:40 DROP UDP 192.168.1.189
239.255.255.250 1037 1900 161 – – – – – – – RECEIVE
2011-04-20 08:42:53 DROP
UDP 192.168.1.189 239.255.255.250 1050 1900 160 – – – – – – –
RECEIVE
2011-04-20 08:42:54 DROP UDP 192.168.1.189 239.255.255.250 1050 1900
161 – – – – – – – RECEIVE
2011-04-20 08:42:54 DROP UDP 192.168.1.189
239.255.255.250 1050 1900 165 – – – – – – – RECEIVE
2011-04-20 08:42:56 DROP
UDP 192.168.1.189 239.255.255.250 1050 1900 161 – – – – – – –
RECEIVE
2011-04-20 08:42:56 DROP UDP 192.168.1.189 239.255.255.250 1050 1900
165 – – – – – – – RECEIVE
2011-04-20 08:42:53 DROP UDP 192.168.1.189
239.255.255.250 1050 1900 161 – – – – – – – RECEIVE
2011-04-20 08:42:53 DROP
UDP 192.168.1.189 239.255.255.250 1050 1900 165 – – – – – – –
RECEIVE
2011-04-20 08:42:54 DROP UDP 192.168.1.189 239.255.255.250 1050 1900
160 – – – – – – – RECEIVE
2011-04-20 08:42:56 DROP UDP 192.168.1.189
239.255.255.250 1050 1900 160 – – – – – – – RECEIVE
2011-04-20 08:42:57 DROP
UDP 192.168.1.189 239.255.255.250 1050 1900 160 – – – – – – –
RECEIVE
2011-04-20 08:42:59 DROP UDP 192.168.1.189 239.255.255.250 1050 1900
160 – – – – – – – RECEIVE
2011-04-20 08:43:00 DROP UDP 192.168.1.189
239.255.255.250 1050 1900 161 – – – – – – – RECEIVE
2011-04-20 08:43:00 DROP
UDP 192.168.1.189 239.255.255.250 1050 1900 165 – – – – – – –
RECEIVE
2011-04-20 08:43:02 DROP UDP 192.168.1.189 239.255.255.250 1050 1900
161 – – – – – – – RECEIVE
2011-04-20 08:43:02 DROP UDP 192.168.1.189
239.255.255.250 1050 1900 165 – – – – – – – RECEIVE
2011-04-20 08:43:04 DROP
UDP 192.168.1.189 239.255.255.250 1050 1900 160 – – – – – – –
RECEIVE
2011-04-20 08:43:05 DROP UDP 192.168.1.189 239.255.255.250 1050 1900
160 – – – – – – – RECEIVE

在www.ip138.com上查了一下239.255.255.250这个IP地址，显示：IANA保留地址用于多点传送，即是一个组播地址（单播、广播、组播微软介绍：http://www.microsoft.com/windows/windowsmedia/cn/serve/multiwp.aspx）。
对IANA不解，用Google搜索了一番，得到如下资料：

IANA (Internet Assigned Numbers Authority)
，Internet号分配机构。负责对IP地址分配规划以及对TCP/UDP公共服务的端口定义。国际互联网代理成员管理局（IANA）是在国际互联网中使用的IP
地址、域名和许多其它参数的管理机构。IP地址、自治系统成员以及许多顶级和二级域名分配的日常职责由国际互联网注册中心（IR）和地区注册中心承担。
在IP地址范围内，非路由地址IANA(InternetAssignedNumbersAuthority)将一部分地址保留作为私人IP地址空间，专门用于内部局域网使用，这些地址如下表：
类IP地址范围网络数
A
10.0.0.0—10.255.255.2551
B 172.16.0.0—172.31.255.25516
C
192.168.0.0—192.168.255.255255
这些地址是不会被Internet分配的，因此它们在Internet上也从来不会被路由，虽然它们不能直接和Internet网连接，但仍旧可以被用来和Internet通讯，我们可以根据需要来选用适当的地址类，在内部局域网中大胆地将这些地址当作公用IP地址一样地使用。在Internet上，那些不需要与Internet通讯的设备，如打印机、可管理集线器等也可以使用这些地址，以节省IP地址资源。