cpw%sneezy@LANL.GOV (C. Philip Wood) (09/02/88)
I'm curious about a packet that shows up every so often on the LANL Internet. The ones I caught were ICMP ECHO requests. What was curious about them was the Type of Service field. In one case the TOS field was '11111110' which maps to Precedence == Network Control Delay == Low Throughput == High Reliablility == High Reserved bit 6 == on Now, I can understand how a particular implimentation would like to have low delay, high throughput and high reliability - wouldn't we all. I also understand that setting more than two of these is considered excessive. However, as I understand it TOS is not something that is actually offered by vendors now or understood to well by the Internet in general. I next, asked the owner of the machine to do a few more echo's, The TOS field varied. The machine is a SUN with IPC board running 3.5. Another interesting fact is that the VMS system running Wollengong TCP/IP software responded with ROUTINE precedence. I tried the same thing with a BSD4.3 system and it also returned the packet, but with the same TOS bits. In either case I would think the responder should drop the packet because of the bit set in the reserved field. I assume that some coder forgot to clear the TOS field. One questions are: Are those reserved bits still reserved and supposed to be zero? And if the are reserved and non-zero, should we drop the packet. Phil Wood, cpw@lanl.gov
barns@GATEWAY.MITRE.ORG (Bill Barns) (09/07/88)
I don't recall seeing any response to this, and the subject is of current interest to me. I am working up an analysis of options for dealing with certain kinds of potential "requirements" for network usage accounting and one of the approaches to be considered for internetwork reverse charging might involve using one of the two reserved bits to which you refer. I believe they are still officially reserved and supposed to be 0. I have contributed to appropriate people the thought that it would be a good thing for a TCP/IP implementor to make provision for setting and reading the two reserved bits even before any meaning is defined for them. It's just as important to have it be settable at TCP/application interface level as at IP/transport interface. One should also consider the possibility that the reserved TOS bits may require a negotiation analogous to precedence. If anyone out there is working in the same problem domain I am, or can point me to such people, please drop me a note. I am especially interested in finding out about anything in the OSI arena subsequent to the Accounting Management Service Definition, TC97/SC21 N981 (alias TC97/SC21/WG4 N117). I've already queried the ISO mailing list but no news so far... Bill Barns / MITRE / barns@gateway.mitre.org / (703) 883-6832