Date: Mon, 23 Nov 1998 18:41:18 +0000 From: "Nick A. Fikouras" <nick@dcs.shef.ac.uk> To: bmah@CA.Sandia.GOV Cc: Andrey Tchoritch <andy@moldsat.md>, "Bruce A. Mah" <bmah@california.sandia.gov>, "freebsd-questions@FreeBSD.ORG" <freebsd-questions@FreeBSD.ORG> Subject: Re: Timestamps and nonces in IP packets Message-ID: <3659AC4E.376CB6A@dcs.shef.ac.uk> References: <199811221910.LAA13033@stennis.ca.sandia.gov>
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Bruce A. Mah wrote: > If memory serves me right, Andrey Tchoritch wrote: > > On Sun, 22 Nov 1998, Bruce A. Mah wrote: > > > If memory serves me right, "Nick A. Fikouras" wrote: > > > > > > > I've noticed while monitoring TCP communications between FBSD machines > > > > that every IP packet contains timestamps and nonces that take up an > > > > extra 40 octets in the packets. Does anybody know how I can turn off > > > > this setting? > > > > > > Haven't seen anyone write an answer to this yet, so: > > > > > > Edit /etc/rc.conf, and set: > > > > > > tcp_extensions="NO" > > > > > > > > > What is this extensions for? > > The timestamp option in the TCP header allows to sender of a TCP segment to > compute the round-trip time (RTT) for every segment sent and acknowledged. It > places a timestamp in every outgoing segment it sends...the receiver (assuming > it support this option) copies this timestamp back to an appropriate field in > the ACK it sends back for that segment. > Why can't the TCP sequence number be used instead. TCP uses that sequence numbers anyway to acknowledge the safe receipt of data. > Without the use of the timestamp extension, the sending TCP can only estimate > the RTT once per round trip. > I thought it always requires a round trip to measure the Round Trip Time. > IIRC, the other option controlled by tcp_extensions is window scaling. This > allows larger TCP congestion windows than the 64K allows by the original > specification, by multiplying the window sizes by an agreed-upon power of 2. > Useful mostly for high-delay, high-bandwidth paths, such as satellite links. > > Bruce. > Thank you for your response Bruce. 8) nick To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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