Path: utzoo!utgpu!water!watmath!clyde!bellcore!faline!thumper!ulysses!ucbvax!CLASH.CISCO.COM!satz
From: satz@CLASH.CISCO.COM
Newsgroups: comp.protocols.tcp-ip
Subject: (none)
Message-ID: <8805221402.AA28612@ucbvax.Berkeley.EDU>
Date: 21 May 88 05:00:46 GMT
References: <8805190058.AA09533@FORD-COS1.ARPA>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 20

Kevin,

Someone was supposed to write up an RFC describing the mapping used for
class B and C addresses. What is currently being used in the cisco DDN X.25
implementation is:

	class A: N.H.L.I
	class B: N.N.H.I
	class C: N.N.N.HI

Where N represents the network number. H represents the PSN port number. L
is the logical host field and is still zero. I is the PSN number. For class
B addresses, the H field uses the unused L field.  For class C addresses,
the H field lies in the upper four bits of the last octet and the I field
in the lower four. I don't know of anyone who has a class C PSN network.

Hope this helps,

Greg Satz
cisco