Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!purdue!decwrl!ucbvax!LANL.GOV!cpw%sneezy
From: cpw%sneezy@LANL.GOV (C. Philip Wood)
Newsgroups: comp.protocols.tcp-ip
Subject: TOS field in IP packet
Message-ID: <8809012229.AA02511@sneezy.lanl.gov>
Date: 1 Sep 88 22:29:49 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 38

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