Re: Problem with TCP/IP echo and K5JB - TCP-IP

This is a discussion on Re: Problem with TCP/IP echo and K5JB - TCP-IP ; In article , Oliver Lehmann wrote: > > echoping -v -w 2 -s 32 -n 1 10.1.1.2 > > This is echoping, version 6.0.0. > > Trying to connect to internet address 10.1.1.2 7 to transmit 32 bytes... > Trying ...

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Thread: Re: Problem with TCP/IP echo and K5JB

  1. Re: Problem with TCP/IP echo and K5JB

    In article <20080419131943.ef31cbfc.lehmann@ans-netz.de>,
    Oliver Lehmann wrote:
    > > echoping -v -w 2 -s 32 -n 1 10.1.1.2

    >
    > This is echoping, version 6.0.0.
    >
    > Trying to connect to internet address 10.1.1.2 7 to transmit 32 bytes...
    > Trying to send 32 bytes to internet address 10.1.1.2...
    > Can't connect to server (Operation timed out)
    > Exit 1
    >
    > tcpdump shows (just an extract):
    >
    > 13:13:28.839003 IP (tos 0x0, ttl 64, id 56001, offset 0, flags [DF],
    > proto TCP (6), length 60) 10.1.1.1.50984 > 10.1.1.2.echo: S,
    > cksum 0xb417 (correct),
    > 903547536:903547536(0) win 65535 > sackOK,timestamp 12024138 0>
    > 0x0000: 0145 0000 3cda c140 0040 0649 f60a 0101 .E..<..@.@.I....
    > 0x0010: 4500 003c dac1 4000 4006 49f6 0a01 0101 E..<..@.@.I.....
    > 0x0020: 0a01 0102 c728 0007 35db 0a90 0000 0000 .....(..5.......
    > 0x0030: a002 ffff b417 0000 0204 0200 0103 0303 ................
    > 0x0040: 0402 080a 00b7 794a 0000 0000 ......yJ....
    > 13:13:29.062298 IP (tos 0x0, ttl 254, id 65456, offset 0, flags [none],
    > proto TCP (6), length 44) 10.1.1.2.echo > 10.1.1.1.50984: S,
    > cksum 0xb461 (correct),
    > 1262663520:1262663520(0) ack 4294967185 win 2048
    > 0x0000: 0045 0000 2cff b000 00fe 06a7 160a 0101 .E..,...........
    > 0x0010: 4500 002c ffb0 0000 fe06 a716 0a01 0102 E..,............
    > 0x0020: 0a01 0101 0007 c728 4b42 b760 ffff ff91 .......(KB.`....
    > 0x0030: 6012 0800 b461 0000 0204 0200 `....a......
    >
    > I don't know how the package the old system sends out should look like
    > but it seems to be wrong - otherwise the echoping would have detected it
    > I'd guess.
    > I've tried other services like telnet and ftp before but they didn't
    > worked either. Thats why I decided to try such easy service like echo.
    >
    > Any ideas whats wrong with my TCP packet the old system sent?


    The sequence number in the SYN is 903547536, so the acknowledgement
    field in the SYN-ACK should be 903547537. But instead it's 4294967185.

    --
    Barry Margolin, barmar@alum.mit.edu
    Arlington, MA
    *** PLEASE don't copy me on replies, I'll read them in the group ***

  2. Re: Problem with TCP/IP echo and K5JB

    In article ,
    Barry Margolin wrote:

    >The sequence number in the SYN is 903547536, so the acknowledgement
    >field in the SYN-ACK should be 903547537. But instead it's 4294967185.


    903547537=0X35db0a91
    4294967185=0Xffffff91

    maybe using an 8-bit, signed type for sequence numbers and suffering
    some sign extension craziness?


    Vernon Schryver vjs@rhyolite.com

  3. Re: Problem with TCP/IP echo and K5JB

    On 2008-04-21 01:54:05 -0400, vjs@calcite.rhyolite.com (Vernon Schryver) said:

    > In article ,
    > Barry Margolin wrote:
    >
    >> The sequence number in the SYN is 903547536, so the acknowledgement
    >> field in the SYN-ACK should be 903547537. But instead it's 4294967185.

    >
    > 903547537=0X35db0a91
    > 4294967185=0Xffffff91
    >
    > maybe using an 8-bit, signed type for sequence numbers and suffering
    > some sign extension craziness?



    Now that's just a brilliant insight, kudos dude.

    /dmfh

    --
    _ __ _
    __| |_ __ / _| |_ 01100100 01101101
    / _` | ' \| _| ' \ 01100110 01101000
    \__,_|_|_|_|_| |_||_| dmfh(-2)dmfh.cx


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