Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!lll-tis!ames!pasteur!ucbvax!CC5.BBN.COM!malis From: malis@CC5.BBN.COM (Andy Malis) Newsgroups: comp.protocols.tcp-ip Subject: Re: IP class B and C to X.25 address translation Message-ID: <8801191938.AA13432@ucbvax.Berkeley.EDU> Date: 19 Jan 88 18:53:06 GMT Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 45 The following message didn't seem to make it out of my host when I sent it the first time. Since this is a topic that comes up from time to time, I thought I would resend it. Andy ------- Forwarded Message To: "Barry D. Hassler" cc: malis,tcp-ip@sri-nic.arpa Subject: Re: IP class B and C to X.25 address translation In-reply-to: Your message of Sun, 27 Dec 00 19:87:13 +0000. <7137.8712280332@wrtfac.cdc.com> Date: Mon, 28 Dec 87 11:44:33 -0500 From: Andy Malis Barry asked the following: Has there been any standardization on the translation of Class B or C IP addresses to X.25 addresses? I am aware of the translation standard for Class A addresses, but have not seen any for B or C. Barry, There is an informal standardization for Class B: the first two octets of the IP address are the network number, the third octet is treated identically to the second octet of Class A addresses, and the fourth octet is treated identically to the fourth octet of Class A addresses. The third octet of Class A addresses is dropped completely in Class B addresses. There is absolutely no standardization for Class C, because there are so few local network address bits to play with. The host network software support person for Class C nets must provide his or her own mapping between the Class C addresses and X.25 addresses for that net. For example, the five most significant bits of the fourth octet of the Class C address could be the host number, and the three least significant bits the PSN number. It is a compromise between the number of PSNs on the network and the maximum number of hosts on a PSN. Regards, Andy ------- End of Forwarded Message