Date: 1 Jul 1996 12:56:12 +0200 From: "Stefan Bethke" <stefan@Promo.DE> To: "FreeBSD Questions" <freebsd-questions@freebsd.org> Subject: TCP time-outs on PPP line Message-ID: <n1375896662.75251@quick.Promo.DE>
next in thread | raw e-mail | index | archive | help
Hi, we are connected through an analog leased line with two USR Courier, = using 2.1.0R and pppd. Since upgrading from Linux we experience some TCP "connection timed out" = failures. It seems that at those moments someone is downloading from our = HTTP or FTP server (looking at the modem leds and = ftpwho/xferlog/http-log). Trying to ping the terminal server of our provider doesn't give a = response; after 5 or so pings, ping says "No buffer space available". My understanding is that the already established TCP connection quickly = fills the output buffer and saturates the line; at this point, a packet = inserted into the queue will be sent after (worst case) mtu / bandwith * = queue length (ifq_maxlen) =3D 1500 / 2880 * 50 =3D 27 seconds. (Or, = taking fastq into account, 54 secs). What's the solution? Possibilities are - reduce ifq_maxlen, so ENOBUF will be returned earlier, so TCP will (hopefully) send slower earlier; - reduce the mtu, so a full queue run will be faster, thereby allowing a = new packet to be sent faster; - devise a mechanism to promote those connections we want to precede our external users' connections to the fastq; possibly by promoting all packets smaller than xxx bytes to fastq; - upgrade to a 2 Mbit line :-) I didn't test any of these yet, because I rather like to have a slow but = working line... Any comments will be greatly appreciated. Stefan Bethke -- Promo Datentechnik | Tel. 040/431360-0 + Systemberatung GmbH | Fax. 040/431360-60 Waterloohain 6-8 | e-mail: stefan@Promo.DE D-22769 Hamburg | http://www.Promo.DE/
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?n1375896662.75251>