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From: brescia@CCV.BBN.COM.UUCP
Newsgroups: mod.protocols.tcp-ip
Subject: Re: IP Record Route in core?
Message-ID: <8702131115.AA23652@ucbvax.Berkeley.EDU>
Date: Thu, 12-Feb-87 09:25:51 EST
Article-I.D.: ucbvax.8702131115.AA23652
Posted: Thu Feb 12 09:25:51 1987
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     *)  The core gateways do not record any route information,

This was a conscious design decision, not to look at any packets which do not
have the IP destination = 'the gateway'.  Well, that's not the whole case,
because the lsi11 gateways will do IP header checksum and other validity
checks, but they will not examine the options unless fragmentation is needed.

The tradeoff was between speed and functionality.  At that time, probably 4
years ago, we went for speed.  At this time, the answer is, "wait for the next
generation".  When faced with the same decision in the butterfly, I lost the
argument, so that will (does?) do record route, but at the expense (for
packets with record route option only) of extra processing at each hop,
because no shortcuts are taken past the full IP network routing.

Note that Source route does have a record route trailer.

     In the BRL gateway, the IP Record Route code is about 20 lines of C...

I expect the 11 could do it with 40 lines of macn11 ... (but it would be wrong).

     *)  There is some ambiguity as to how to interpret the combination
     of ICMP ECHO REQUEST and IP Record Route together.  The Mills Fuzzball
     software seems to regard the ICMP ECHO REPLY as a separate transaction,
     and resets the Record Route pointer to the beginning of the log area,
     while the BRL Gateway presently continues recording, so you see
     the full route, round trip.  There is merit to both, is one considered
     "right"?

This could become an emotional issue of 'right vs. wrong' but I think that
more information is provided by NOT resetting the pointer.  By the way, should
the echoing host also do a record route?  Remember it's a host, not a gateway
function.

Mike B.