Date: Tue, 11 Apr 1995 15:28:54 +0200 From: Andras Olah <olah@cs.utwente.nl> To: questions@FreeBSD.org Subject: Re: Does BSD implement TCP/IP incorrectly? Message-ID: <8003.797606934@utis156.cs.utwente.nl> In-Reply-To: Your message of Tue, 11 Apr 1995 07:04:17 EDT
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On Tue, 11 Apr 1995 07:04:17 EDT, Denis Fortin wrote: > As far as I know, it has to do with the datagram sequence numbers used > in TCP connections. BSD TCP/IP always starts the sequence number at 1 > (thereby making it relatively easy to guess that within a few moments of > a connection, the number will be 2, 3, 4, etc.) > > If I recall properly, the relevant RFCs specify that these numbers are > supposed to be randomly chosen. Always picking "1" can probably be > construed as being somewhat predictable and less that random (!). > > Now, I'm quoting all of this from memory, so any TCP/IP gurus out > there are welcome to jump in and correct me! I don't consider myself a guru, but the situation is that tcp_iss is initialized to 1 ONLY at bootup time. After that, tcp_iss is incremented by 64000 twice a second and every time a TCP connection is opened. You can easily check this out by reading the code in /sys/netinet or by running `tcpdump -S' for a few minutes. (See also Wright-Stevens: TCP/IP Illustrated, vol 2.) Andras
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