关于广播路由的问题

huahd

Look at the following subnet, how many packets are generated by a broadcast from B, using reverse path forwarding?
http://tkfiles.storage.live.com/ ... TwWIDckP7W-kJy-dMsA

this is the 14th problem of chapter 5 of Tanenbaum's Computer Networks, 4th edition. and the answer, according to the book's solutions manual, is 21. however, i think it should be 28.
can anyone help me?
thanks a lot!

请看下图所示的子网，现使用逆向路径转发算法从B广播一条消息，问共产生了多少个分组。
http://tkfiles.storage.live.com/ ... TwWIDckP7W-kJy-dMsA

这是Tanenbaum的名著《计算机网络》（第四版）当中第五章的第14题，作者伴随教材出版的习题解答当中说答案是21，但我得出的结果却是28。大家一起讨论一下？