From owner-freebsd-questions Fri Dec 1 08:23:13 1995 Return-Path: owner-questions Received: (from root@localhost) by freefall.freebsd.org (8.6.12/8.6.6) id IAA06907 for questions-outgoing; Fri, 1 Dec 1995 08:23:13 -0800 Received: from halloran-eldar.lcs.mit.edu (halloran-eldar.lcs.mit.edu [18.26.0.159]) by freefall.freebsd.org (8.6.12/8.6.6) with SMTP id IAA06898 for ; Fri, 1 Dec 1995 08:23:08 -0800 Received: by halloran-eldar.lcs.mit.edu; (5.65/1.1.8.2/19Aug95-0530PM) id AA13050; Fri, 1 Dec 1995 11:20:28 -0500 Date: Fri, 1 Dec 1995 11:20:28 -0500 From: "Garrett A. Wollman" Message-Id: <9512011620.AA13050@halloran-eldar.lcs.mit.edu> To: Brian Tao Cc: questions@FreeBSD.org Subject: Re: What is in_rtqtimo ? In-Reply-To: References: <9511301605.AA08576@halloran-eldar.lcs.mit.edu> Sender: owner-questions@FreeBSD.org Precedence: bulk < said: >[I wrote:] >> The parameters are all tunable, in the net.inet.ip branch of the MIB: >> >> net.inet.ip.rtexpire = 3600 # current max lifetime >> net.inet.ip.rtminexpire = 10 # minimum max lifetime >> net.inet.ip.rtmaxcache = 128 # how many is ``too many'' > On servers that see a lot of connections from different hosts > coming and going (like on our IRC server), would turning up the > rtexpire and or rtmaxcache values be a good thing to do? It's difficult to say; it depends a lot on whether any useful statistics are getting saved in the cache. If you see a significant amount of Transaction TCP traffic, increasing rtmaxcache or rtminexpire might help. Be aware that every entry costs on the order of 256 bytes of memory, which is why we make an effort to dynamically limit them in the first place. You can tell whether you are getting useful statistics by looking at the output of `netstat -p tcp' and searching for the following: 181 connections closed (including 19 drops) 27 connections updated cached RTT on close 27 connections updated cached RTT variance on close 5 connections updated cached ssthresh on close You can examine the statistics by using the `route get' command; for example: ------------------------------------ root@khavrinen(17)# route get freefall.freebsd.org route to: freefall.FreeBSD.ORG destination: freefall.FreeBSD.ORG gateway: radole interface: ed0 flags: recvpipe sendpipe ssthresh rtt,msec rttvar hopcount mtu expire 16384 16384 1656 438 500 0 1500 3538 ------------------------------------ The ssthresh value is the switchover point between linear and exponential TCP window expansion; rtt is the estimated round-trip time; and rttvar is the ``variance'' of the rtt measurement. (I put `variance' in quotes because the value is not computed as a true statistical variance, but rather as an average deviation.) A correct ssthresh value can substantially increase the performance of short connections; rtt and rttvar come into play when determining how long to wait for an acknowledgement before timing out and retransmitting the packet. -GAWollman -- Garrett A. Wollman | Shashish is simple, it's discreet, it's brief. ... wollman@lcs.mit.edu | Shashish is the bonding of hearts in spite of distance. Opinions not those of| It is a bond more powerful than absence. We like people MIT, LCS, ANA, or NSA| who like Shashish. - Claude McKenzie + Florent Vollant