Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!rutgers!topaz.rutgers.edu!hedrick From: hedrick@topaz.rutgers.edu (Charles Hedrick) Newsgroups: comp.unix.wizards Subject: Re: Trouble with Ethernet Message-ID: <15078@topaz.rutgers.edu> Date: Sat, 26-Sep-87 17:01:59 EDT Article-I.D.: topaz.15078 Posted: Sat Sep 26 17:01:59 1987 Date-Received: Sun, 27-Sep-87 11:14:48 EDT References: <9473@brl-adm.ARPA> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 63 I'm not sure why people responded to this question again, since you just quoted it on order to make another point, but let me point out that the answers given by both ron and ted, although generally correct, would leave someone with an incorrect idea of how to cause his machine to talk to net 126. The correct way is route add 126.0.0.0 0 where is your machine's own Internet address. Ron's example used route add 128.8.8.0 ... which treated a class B network (128.8) as if it were class C. Ted's message (1) gave examples only for class C nets, and (2) stated that 126 was a class B address, when it is actually class A. I assume this is all a matter of typos. I'm sure that these people all know what the classes are. But for those who don't: these is no network 0. Addresses beginning with 0 are reserved for use by machines that don't know their own address. networks 1 through 126 are "class A". They are designed for commerical networks or very large companies, who need 3 bytes to describe their internal networks. Addresses are of the form 10.1.0.89 where 10 is the network number, and 1.0.89 designates the specific host. (By the way, network number 126 is reserved for use by the Central University of Mars, for which reason packets that escape into the Arpanet with addresses on net 126 are referred to as "Martians". By analogy, this term is also used for all packets containing unauthorized or inappropriate addresses. A "Martian filter" is a software test for testing for and rejecting inappropriate addresses.) network 127 is also class A, but is reserved for use by the "loopback" interface. networks 128.1 through 191.254 [note that there is no 128.0, and I trust there will be no 191.255, to avoid confusion] are class B. They are typically used by fairly large universities and companies, who need 2 bytes to describe their internal networks. Addresses are of the form 128.6.4.194 where 128.6 is the network number and 4.194 designates the specific host on that network. networks 192.1.1 through 223.254.254 are class C. These are designed for single departments or small organizations, for which 254 possible addresses is enough. (As usual, 0 and 255 are not used.) Addresses are of the form 192.12.88.3 where 192.12.88 is the network number and 3 designates the specific host on that network. addresses beginning with 224 through 254 are reserved for "class D" and "class E", which are currently not defined. It is common for software to treat all addresses 192 and above as class C. Properly speaking, addresses between 224 and 254 should be treated as Martian. addresses beginning with 255 are reserved for use as broadcast addresses. In the "route add" command (or other commands), where a "network number" is wanted, you must give an address which has 0's filled in for the host portion. E.g. to specify network 128.6, you would use 128.6.0.0. For network 126, you must use 126.0.0.0. If you use 126.8.8.0, it will look like a specific host, and you will get a "host route", which is not at all what you want. These rules can be changed by using the "subnet mask" command in ifconfig, but I am assuming, based on the obvious unsophistication of the original question, that this was not being done.