Why o Why
Page 1 of 2 12 LastLast
Results 1 to 10 of 16

Thread: Why o Why

  1. #1
    Senior Member
    Join Date
    Jan 2004
    Posts
    199

    Why o Why

    Why o Why is is there 65,535 ports ? Why not 65,536 or 65,534 ? Does anyone know ?
    -

  2. #2
    Senior Member
    Join Date
    Jan 2004
    Posts
    199
    Thanks Alot Dude !
    -

  3. #3
    Senior Member Maestr0's Avatar
    Join Date
    May 2003
    Posts
    604
    I believe its because the TCP packet header only allows for a 16-bit port numer (source and destination) so 0-65535 is the number range you get.


    -Maestr0
    \"If computers are to become smart enough to design their own successors, initiating a process that will lead to God-like omniscience after a number of ever swifter passages from one generation of computers to the next, someone is going to have to write the software that gets the process going, and humans have given absolutely no evidence of being able to write such software.\" -Jaron Lanier

  4. #4
    Yes, that's my CC number! 576869746568617's Avatar
    Join Date
    Dec 2003
    Location
    Earth
    Posts
    397
    You're on the right track Maestr0. It's a 32 bit addressing scheme though, and it uses 32 bit header information (TCP packet header uses a 32-bit port number), not 16bit.

    65535 just happens to be the highest positive number that can be obtained using 32 bits.

    That's also why the portons of an IP and subnet mask are called octets. (8bits per octet x 4 octets = 32bit Address)

    This limitation is addressed in IPv6.....If they ever finalize it!
    Windows 9x: n. A collection of 32 bit extensions and a graphical shell for a 16 bit patch to an 8 bit operating system originally coded for a 4 bit microprocessor. Written by a 2 bit company that can\'t stand 1 bit of competition.


  5. #5
    Senior Member Maestr0's Avatar
    Join Date
    May 2003
    Posts
    604
    The 32-bit adress is related to the IP portion of the protocol(s) and does not contain any information about ports. The TCP portion of the packet contains two 16-bit fields in the header, one for the source port and one for the destination port.

    -Maestr0
    \"If computers are to become smart enough to design their own successors, initiating a process that will lead to God-like omniscience after a number of ever swifter passages from one generation of computers to the next, someone is going to have to write the software that gets the process going, and humans have given absolutely no evidence of being able to write such software.\" -Jaron Lanier

  6. #6
    AO BOFH: Luser Abuser BModeratorFH gore's Avatar
    Join Date
    Oct 2002
    Location
    Michigan
    Posts
    7,177
    To me it's kind of like 255. You can't have an IP passed that...or Subnet mask. There are actually only 254 useable though, because 255 is 11111111 in binary, and is not useable, and 0 is of course the other value, and is also not useable....Ok, I know what I'm talking about here but I just crawled out of bed and I'm still waking up, anyone want to clarify this better untill I'm awake?
    Kill the lights, let the candles burn behind the pumpkins’ mischievous grins, and let the skeletons dance. For one thing is certain, The Misfits have returned and once again everyday is Halloween.The Misfits FreeBSD
    Cannibal Holocaust
    SuSE Linux
    Slackware Linux

  7. #7
    The Doctor Und3ertak3r's Avatar
    Join Date
    Apr 2002
    Posts
    2,744
    Ahhhh hang on thar a moment..

    65535 just happens to be the highest positive number that can be obtained using 32 bits.
    if you check your binary.. 65535 is the highest value that can be obtained from 16bits..
    If my history comes correctly the 64k ports comes from the 8bit cpu days where the original systems could only address 65535bytes.. the cpu would work addresses in 16 bit values..
    the X25 protocol was 8bit based and was used with early TCP work..

    maestr0 has it:
    The 32-bit adress is related to the IP portion of the protocol(s) and does not contain any information about ports. The TCP portion of the packet contains two 16-bit fields in the header, one for the source port and one for the destination port.
    Cheers
    "Consumer technology now exceeds the average persons ability to comprehend how to use it..give up hope of them being able to understand how it works." - Me http://www.cybercrypt.co.nr

  8. #8
    Yes, that's my CC number! 576869746568617's Avatar
    Join Date
    Dec 2003
    Location
    Earth
    Posts
    397
    I just brushed over my TCP/IP and you are correct, Maestr0...the TCP portion of the packet does contain 16-bit, not 32bit headers. Also, I did the binary and Und3ertak3r is correct also.

    I guess I was thinking IPv4 is 32-bit and not thinking about the fact that it still uses the original 16-bit addressing scheme.
    Windows 9x: n. A collection of 32 bit extensions and a graphical shell for a 16 bit patch to an 8 bit operating system originally coded for a 4 bit microprocessor. Written by a 2 bit company that can\'t stand 1 bit of competition.


  9. #9
    does the port begin with 0000 ????

  10. #10
    Senior Member
    Join Date
    Jan 2004
    Posts
    199
    No .... port 1 i think , best if one of the mods or senior members comfirm tho Thanks
    -

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

 Security News

     Patches

       Security Trends

         How-To

           Buying Guides