Path: utzoo!utgpu!water!watmath!clyde!att-cb!ucbvax!SEISMO.CSS.GOV!rick
From: rick@SEISMO.CSS.GOV (Rick Adams)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  SLIP working group?
Message-ID: <8803302259.AA28640@beno.CSS.GOV>
Date: 30 Mar 88 22:59:24 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 48


If you are going to add multiple protocol support to SLIP, please do it
in the following manner.

The first byte following a FRAME_END is the protocol type byte.

If the byte is 0x40 - 0x4F the packet is considered to be an IP packet
and the protocol type byte IS INCLUDED as part of the packet.
(Astute observers will realize that this is an IP Version Number of 4
combined with all of the possible IP header lengths.)

Otherwise, the protocol type byte selects a protocol family from the
following table (stolen from socket.h on 4.3BSD) and the protocol type
byte IS NOT INCLUDED as part of the packet.

This will allow "old" SLIP implementations to talk to your new system
without modification. It also provides all of the functionality you
might need. If you feel that you MUST have error detection, error
correction, header compression, or even encryption, please define a new
address family number and add it to the table. That way those who
feel it is not necessary will not be burdend with it and everyone is
happy.

It should be very easy to implement. I'd do it, but I have no need for
multiple protocols.

---rick

/*
 * Address families.
 */
#define	AF_UNSPEC	0		/* unspecified */
#define	AF_UNIX		1		/* local to host (pipes, portals) */
#define	AF_INET		2		/* internetwork: UDP, TCP, etc. */
#define	AF_IMPLINK	3		/* arpanet imp addresses */
#define	AF_PUP		4		/* pup protocols: e.g. BSP */
#define	AF_CHAOS	5		/* mit CHAOS protocols */
#define	AF_NS		6		/* XEROX NS protocols */
#define	AF_NBS		7		/* nbs protocols */
#define	AF_ECMA		8		/* european computer manufacturers */
#define	AF_DATAKIT	9		/* datakit protocols */
#define	AF_CCITT	10		/* CCITT protocols, X.25 etc */
#define	AF_SNA		11		/* IBM SNA */
#define AF_DECnet	12		/* DECnet */
#define AF_DLI		13		/* Direct data link interface */
#define AF_LAT		14		/* LAT */
#define	AF_HYLINK	15		/* NSC Hyperchannel */
#define	AF_APPLETALK	16		/* Apple Talk */