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To: Jim Fleming <JimFleming@unety.net>
cc: hackers@freebsd.org
Subject: Re: Check IP Version 
In-reply-to: Your message of "Sat, 06 Apr 96 22:28:56 PST."
             <01BB2419.36344C40@webster.unety.net> 
Date: Mon, 8 Apr 1996 09:51:22 PDT
From: Bill Fenner <fenner@parc.xerox.com>
Message-Id: <96Apr8.095128pdt.177476@crevenia.parc.xerox.com>
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In message <01BB2419.36344C40@webster.unety.net> you write:
>It is not desirable for new versions of IP to "break" existing code. I have not
>provide this but in studying the SLIP code I see that there is never really
>a check done to see of the IP header is of version 4.

If you are running SLIP, then it is carrying IPv4.  Run PPP if you want to
do different protocols on one link.

Note that the IPv6 people decided that there were too many broken
implementations that don't check the IP version number, so they decided
to get a new ethertype to carry IPv6 frames.

  Bill