Date: Mon, 12 Jul 2010 20:02:44 +0300 From: Andrei Kolu <antik@bsd.ee> To: freebsd-stable@freebsd.org Subject: Re: bogus DSCP value for ssh Message-ID: <AANLkTinY9ejDZEoa9TiJyd64-UfJLykZXfEhSYv_zYyS@mail.gmail.com> In-Reply-To: <20100712150147.542BE1CC0D@ptavv.es.net> References: <AANLkTimR7B6SDkD_fbI5O_ggW5UQ8z7SLfgMlNbZF8p2@mail.gmail.com> <20100712150147.542BE1CC0D@ptavv.es.net>
next in thread | previous in thread | raw e-mail | index | archive | help
2010/7/12 Kevin Oberman <oberman@es.net>: >> From: Andrei Kolu <antik@bsd.ee> >> Date: Mon, 12 Jul 2010 15:31:58 +0300 >> Sender: owner-freebsd-stable@freebsd.org >> >> Hi! >> >> I am testing FreeBSD 8.1-RC2 amd64 networking stuff and notice one >> strange DSCP message with wireshark: >> ------------------------------------ >> Internet Protocol, Src: 192.168.1.111 (192.168.1.111), Dst: >> 192.168.1.101 (192.168.1.101) >> Differentiated Services Field: 0x10 (DSCP 0x04: Unknown DSCP; ECN: 0x00) >> 0001 00.. = Differentiated Services Codepoint: Unknown (0x04) >> .... ..0. = ECN-Capable Transport (ECT): 0 >> .... ...0 = ECN-CE: 0 >> >> Transmission Control Protocol, Src Port: ssh (22), Dst Port: >> attachmate-s2s (2419), Seq: 2902917, Ack: 29842, Len: 132 >> ------------------------------------ >> >> There is no firewall enabled. Only thing I changed (should have no >> effect) was: "net.inet.tcp.ecn.enable: 1" >> _______________________________________________ > > I don't know why Wireshark does not understand this, but it is defined > in RFC2474 as Class Selector 2 or simply IP precedence of 2 (of 7). > > If you add the ECN bit, you have Assured Forwarding at IP priority 2. > > Whether you pass or respond to the DSCP bits is, of course, a personal > choice, but there is nothing unusual with this and ssh has bee setting > the bit for a long time. > -- My calculations (X is not used and always zero): 000|100|00 421|21X|00 ---------------- 000|200|00 11= high drop probability 10= medium drop probability 01= low drop probability So "Per-hop behavior" is 000binary= 0decimal and "Drop probability" is 10 binary=2 decimal="Medium drop probability". There is no such a DSCP drop probability value as 4 in existence. I think Wireshark is incorrect but how it is possible to define 000100 at all is beyound me- 000000 is "best effort" already. It is AF02? Yet another bogus priority value? Correct me if I'm wrong. Andrei
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?AANLkTinY9ejDZEoa9TiJyd64-UfJLykZXfEhSYv_zYyS>