Date: Mon, 2 Jun 1997 19:21:03 -0700 From: Ben Cottrell <benco@ucsee.EECS.Berkeley.EDU> To: freebsd-hackers@freebsd.org Subject: Network queueing policy Message-ID: <199706030221.TAA08825@ucsee.EECS.Berkeley.EDU>
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I'm encountering unexpected behavior with FreeBSD 3.0-970209-SNAP (although reports from friends lead me to believe that this problem is universal). The symptom is that apparently it doesn't pay attention to the TOS field. I started an ftp of a large file (ftp is known to set TOS), and then did a series of traceroutes to a machine across a dialup (SLIP) link: > traceroute -w 16 128.32.64.1 traceroute to 128.32.64.1 (128.32.64.1), 30 hops max, 40 byte packets 1 annex-64-1.Berkeley.EDU (136.152.64.2) 3109.643 ms 3472.490 ms 2100.206 ms [etc...] > traceroute -t 16 -w 16 128.32.64.1 traceroute to 128.32.64.1 (128.32.64.1), 30 hops max, 40 byte packets 1 annex-64-1.Berkeley.EDU (136.152.64.2) 3172.278 ms 2005.359 ms 2055.619 ms [etc...] > traceroute -t 8 -w 16 128.32.64.1 traceroute to 128.32.64.1 (128.32.64.1), 30 hops max, 40 byte packets 1 annex-64-1.Berkeley.EDU (136.152.64.2) 2909.118 ms 1867.503 ms 2187.625 ms [etc...] You will note that within tolerance, the round-trip time to get across the SLIP link is constant no matter what the TOS is set to. With normal TOS-dependent routing policy, however, the one using -t 16 should have experienced far less latency. This is corroborated by telnet sessions which get very, very sluggish when anyone is ftping. The MTU is 296, which is an IMHO reasonable value; the baud rate on the tty is 19200. Unfortunately, the modem is an internal ISA one (USR Sportster 33.6)--don't hit me, it came with the pre-packaged PC. The router on the other end is known to do TOS-dependent queueing; the same setup (with a different modem, of course) works *flawlessly* on my Sun 3/50 running NetBSD/sun3. No added latency. Any suggestions as to what causes this and how to improve it would be *greatly* appreciated--needless to say, I don't find this particularly acceptable behavior :-) ~Ben
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