HI All, thanx. Interesting reading. I'm following this tut, http://www.sns.ias.edu/~jns/?pagename=Rules and have a question about the below. Why does the author use /4 for both.? Shouldn't the 1st 1 be /3.? I'm also studying CCNA and thought it looked wrong. Anyway, besides that, it's a good learning site. Kudos to the author, indeed. Cheers. Mark Sargent. CLASS_D_MULTICAST="224.0.0.0/4" CLASS_E_RESERVED_NET="240.0.0.0/4"