Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!rpi!uupsi!sunic!ugle.unit.no!nuug!ifi!enag From: enag@ifi.uio.no (Erik Naggum) Newsgroups: comp.protocols.tcp-ip Subject: Re: Unused portion of first octet? Message-ID: Date: 20 May 91 23:54:23 GMT References: <1991May20.160942.24296@homecare.COM> Sender: enag@ifi.uio.no (Erik Naggum) Organization: Naggum Software, Oslo, Norway Lines: 54 In-Reply-To: jessea@homecare.COM's message of 20 May 91 16: 09:42 GMT Jesse W. Asher writes: | | Correct me if I'm wrong, but Class A-C networks depend on the number of | the first octet in the address. Class A is 1-127, Class B is 128-191, | and Class C is 192-223. What happens to 224-254? What are these being | used for, or are they being used for anything? Just a curious mind | wanting to know. The Internet Numbers RFC [1] contains the authoritative reference on network numbers. Snipped from this vast RFC is the following: [2] The fourth type of address, class D, is used as a multicast address [13]. The four highest-order bits are set to 1-1-1-0. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1 1 1 0| multicast address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Class D Address Note: No addresses are allowed with the four highest-order bits set to 1-1-1-1. These addresses, called "class E", are reserved. -------------- [3] Other Reserved Internet Addresses * Internet Address Network Reference - ---------------- ------- ---------- 224.000.000.000-239.255.255.255 Multicast [JBP] 240.000.000.000-255.255.255.255 Reserved [JBP] -------------- Hope this helps. References: [1] RFC 1166 Kirkpatrick, S.; Stahl, M.K.; Recker, M. Internet numbers. 1990 July; 182 p. (Format: TXT=566778 bytes) (Obsoletes RFC 1117, RFC 1062, RFC 1020) [2] ibid, page 4 [3] ibid, page 100 -- Erik Naggum Professional Programmer +47-2-836-863 Naggum Software Electronic Text 0118 OSLO, NORWAY Computer Communications