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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.unix-wizards,net.dcom
Subject: Re: if_addrlist in AF_INET domain
Message-ID: <1014@umcp-cs.UUCP>
Date: Fri, 18-Apr-86 13:10:10 EST
Article-I.D.: umcp-cs.1014
Posted: Fri Apr 18 13:10:10 1986
Date-Received: Mon, 21-Apr-86 03:24:45 EST
References: <877@harvard.UUCP>
Organization: Computer Sci. Dept, U of Maryland, College Park, MD
Lines: 51
Xref: watmath net.unix-wizards:17719 net.dcom:1820

In article <877@harvard.UUCP>, dyer@harvard.UUCP (Steve Dyer) writes:
>I'm a little confused by the addition of lists of addresses for each
>network interface in the 4.3BSD (beta) release.  [...] Could someone
>describe in a nutshell what additional capabilities this change gives
>us?

In a word: AF_NS.

In more words: the list of addresses holds all the addresses in each
address family.  This is because each family may well have a different
address format: e.g., Internet four-byte `dot' numbers vs. Xerox NS
six-byte Ethernet addresses.  (I wonder what DECNET uses?)

The structure looks like this:

	-----------------           ---------------
	| AF_INET addrs |----\      | AF_NS addrs |----\
	-----------------    |      ---------------    |
			     |                         |
 ----------------            v                         v
 | Ethernet I/F |   ------------------       ------------------
 |     il0      |   | if_addr struct |       | if_addr struct |
 | if_addrlist -+-->|  ... if_next  -+------>|  ... if_next  -+---> ...
 ----------------   ------------------       ------------------
  (struct ifnet)    | INET dependent |       | XNS dependent  |
		    |      data      |       |      data      |
		    |      ....      |       |      ....      |
	(struct ->  |    ia_next     |       |    ia_next     |  <- (struct
	 in_ifaddr) ---------+--------       ----------+-------    ns_ifaddr)
			     |                         |
			     |                         |
 ----------------            v                         v
 | Ethernet I/F |   ------------------       ------------------
 |     il1      |   | if_addr struct |       | if_addr struct |
 | if_addrlist -+-->|  ... if_next  -+------>|  ... if_next  -+---> ...
 ----------------   ------------------       ------------------
		    | INET dependent |       | XNS dependent  |
		    |      data      |       |      data      |
		    |      ....      |       |      ....      |
		    |    ia_next     |       |    ia_next     |
		    ---------+--------       ----------+-------
			     |                         |
			     .                         .
			     .                         .
			     .                         .

(Obviously I am not an ASCII artist.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1415)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu