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From: tcp-ip-RELAY@SRI-NIC.ARPA (William Morgart)
Newsgroups: mod.protocols.tcp-ip
Subject: IP source routing questions
Message-ID: <8610091539.AA16270@mitre-gateway.arpa>
Date: Thu, 9-Oct-86 11:39:47 EDT
Article-I.D.: mitre-ga.8610091539.AA16270
Posted: Thu Oct  9 11:39:47 1986
Date-Received: Thu, 9-Oct-86 21:03:00 EDT
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Approved: tcp-ip@sri-nic.arpa


	After reading the previous messages on IP routing options I thought
I'd mention a few problems with those messages. All of the problems
are caused by the differences between RFC791, The DARPA Internet Protocol
Specification, and MILSTD-1777, The DoD Military Standard Internet Protocol.

	The earlier messages stated that the destnation address
in the IP header is changed at intermedate gateways that are in the source
route list. This is only true if the IPs are implemented according to the RFC.
If the IP was implemented following the MILSTD, it will not change the
header. This is a little gotcha that must be watched since an implementation
meant for the DoD world of MILNET will be required to meet
the MILSTD and not the RFC.

	Another gotcha also relating to options processing is what
options are copied on fragmentation. In the RFC the
"Loose Source and Record Route" option is specified as being copied while
in the MILSTD it isn't copied. Even the MILSTD is confused on this point
since it defines the most significant bit of the option to be the copy flag
and the option type for LSRR is 0131 (octal) though the text in the MILSTD
specifies that LSRR isn't copied.

	Next, the security option as specified in both the RFC and the
MILSTD has been superseded by a new security option developed by the 
IPSO Working Group in early 1985. A document describing the new option
should be available for DCA or DDN.

	Finally, a comment for thought: since DoD via DARPA is paying for
the ARPANET and MILNET plus requiring that MILNET use the MILSTD verison
of IP, the ARPANET side of the world should think about using
the MILSTD version also. If this doesn't happen the two sides won't
be able to interoperate. 

Bill Morgart
bmorgart@mitre-gateway.arpa
Phone: (703) 883-6554