Concerning unused options in IP packets.


JOHNSON%northeastern.csnet@CSNET-RELAY.ARPA
Tue, 1 Apr 86 08:24 EST


     I'm just learning tcp/ip myself. In reading rfc 791, I found the
following general statement in section 3.2:

     "In general an [IP] implementation must be conservative in its
sending behavior, and liberal in its receiving behavior."

     Concerning assumptions about IP packet option formats this seems
like a VERY good idea. To protect one's own system, one should hope for
good input but expect problems with incoming packets. In general I've
found this to be the best way with most software. Yes it's more work
and on some systems it can be very difficult. However, covering your
tail pointer is usually a good idea. It can be very embarrassing to
have your wonderful, totally cosmic piece of software crash in public.
It's even more embarrassing when a real-time system like network goes
down because you drop packets on the floor and then have to get a broom
and a bucket to clean things up. At the speeds and traffic level of
some parts of the network, the mess can get really big FAST.

     I don't know about anyone else but I don't think I'd assume
anything about what options look like in a packet. We all know what
happens when assumptions are made.

Chris Johnson
Sr System Programmer
Northeastern University



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