Date: Sun, 9 Nov 1997 11:54:20 PST From: Bill Fenner <fenner@parc.xerox.com> To: Joe McGuckin <joe@via.net> Cc: hackers@freebsd.org Subject: Re: TCP questions Message-ID: <97Nov9.115426pst.177476@crevenia.parc.xerox.com> In-Reply-To: Your message of "Sun, 09 Nov 97 00:35:42 PST." <199711090835.AAA14711@monk.via.net>
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Joe McGuckin <joe@via.net> wrote: > 48: 2000 1d0c 0000 0204 05b4 05b4 ........... > >What the heck is that other 0x05b4 in the data stream ? I never see >in on the receiving end... It's padding. Look at the IP length. >Can ACK or SYN packets carry application level data as well ? Yes. Almost every packet after the establishment of a TCP connection is an ACK packet. >Is this sending a bunch of nulls to the other telnet client ? No. Look at the IP length. The first "0000" is the TCP urgent pointer (the end of the TCP header), and the IP packet ends there; the futher "0000"'s are padding. >How does the push flag work? If the packet is less than the segment >size and the push flag is zero, does that mean that there's no >payload ? If the push flag is off, it means "you may delay 'pushing' this data up to the receiving user"; if it's on it means to deliver the data to the receiver as soon as possible. Use the IP length to determine how much payload there is. Bill
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