Aucbvax.2319
fa.unix-wizards
utzoo!duke!decvax!ucbvax!KLH@SRI-KL
Thu Jul 16 19:16:44 1981
Re:   BBN SYS.115 'Net Kernel bug
From: KLH at SRI-KL
	It seems to me that the bug you mention (masking imp.link with
0177 instead of 0377) needs a better fix than just changing the mask.
I don't know how similar my arpanet code is to yours, but the
"incontab" routine, which "imphostlink" calls, expects the 200 bit to
tell it whether the link is for a read or write socket.  The right
thing to do if you see the 200 bit on at that point in imp_input is to
reject the message, since according to RFC 739 (page 490 of the
Protocol Handbook), only the values 0 and 2-107 are allowed for NCP
host-host protocol messages.  The current strategem of masking the 200
bit out will probably confuse the NCP if some site sends alien
protocol messages to it (e.g. internet protocol), but this hasn't
appeared to cause problems for my site yet.  (I got my code from Noel
about 2 years back.)
	 Of course, if the BBN version of incontab accepts a full byte
of link-number value (the better to handle non-NCP protocols) and
hacks the read/write specification in some other way, then the mask
fix is of course correct.  (Actually it would be unnecessary to mask
at all since imphostlink does the 0377 masking as well, but again
maybe you have a different piece of code).

--Ken
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