Path: utzoo!attcan!uunet!husc6!uwvax!rutgers!apple!bionet!agate!ucbvax!JESSICA.STANFORD.EDU!almquist From: almquist@JESSICA.STANFORD.EDU (Philip Almquist) Newsgroups: comp.protocols.tcp-ip Subject: Re: Needed: timeouts for connections to dead/dying hosts Message-ID: <8811270536.AA17358@ucbvax.Berkeley.EDU> Date: 27 Nov 88 03:57:00 GMT References: <196@bnr-fos.UUCP> Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 33 Tom, > ... Timeout of an active connection > on the demise of a remote host will take until all 12 retransmission inter- > vals have expired, i.e. <= (12*TCPTV_MAX = 360s)... > 6 minutes to timeout on unacknowledged traffic? Sounds kind of high... If you get a more recent version of 4.3BSD, I think you'll find that the timeout is considerably higher than that now. What would be the point of having a shorter timeout? If you decide that your telnet connection has lost it, you are perfectly free to abort it yourself, even if the operating system hasn't yet decided the connection is dead. Impatient applications that run without human operators ar similarly free to make their own decisions about the usefulness (or lack thereof) of a TCP connection. Why not have a shorter timeout? Well, suppose that some evening you left an ftp running on your system, retrieving some huge file from somewhere several continents away. You might be rather annoyed if you came in the next morning and discovered that the transfer had been aborted because some gateway crashed and your TCP timed the connection out while the gateway was rebooting. Indeed, some would say that this argument suggests that TCP should never time out connections. I'm not sure that they're wrong... Even if they are wrong, it's important to keep in mind that the Internet is growing at a phenomenal pace. Many early implementors of TCP chose "reasonable" upper bounds on round trip times; several years of Internet growth later, those systems were performing very badly and people were calling those same upper bounds "unreasonable" (and various unprintable things). Don't make the same mistake! Philip