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hey there is a conflict then......

Discussion in 'Networks' started by kobem, Dec 28, 2007.

  1. kobem

    kobem Megabyte Poster

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    this is from tcpipguide

    Next Header





    Next Header: This field replaces the Protocol field and has two uses. When a datagram has extension headers, this field specifies the identity of the first extension header, which is the next header in the datagram. When a datagram has just this “main” header and no extension headers, it serves the same purpose as the old IPv4 Protocol field and has the same values, though new numbers are used for IPv6 versions of common protocols. In this case the “next header” is the header of the upper layer message the IPv6 datagram is carrying. See below for more details.

    and from wikipedia

    Next header - Specifies the next encapsulated protocol. The values are compatible with those specified for the IPv4 protocol field (8 bits).

    according to tcpipguide , payload(data not protocol ) is in "NEXT HEADER field" though due to
    wikipedia NEXT HEADER just carries the "protocol of the payload" then
    looking at this schema

    [​IMG]

    wHICH ONE IS TRUE?

    --------------****is payload(data) in next header or under destination address?*****-------------

    ......................................................

    second

    it is said that ipv6 "main header " format consists of version , flow label , payload length ,
    next header , hop limit , traffic class ,source address and dest.address.

    question : --------****** it says main header but why is "the next header" in it?****** ---------it has to be out of
    main header i think
     
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  2. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Read them again more carefully. They are both saying the same thing, but in different words. And the TCPIPGuide has far more detail, including diagrams on how the next-header chain works.

    The next-header field is there as an indication of what the next part is. The whole scheme is done like this to allow the easy disassembly of a headers/packet combination.

    Harry.
     
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  3. kobem

    kobem Megabyte Poster

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    shortly
    1- "is payload(data) under destination address field?"

    2- "main header >>> version , traffic class , flow label , payload length , hop limit ,source
    ve dest. address "

    ext header(s) outside of main header in next header?

    data ?
     
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  4. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Data will appear after all the headers.
    You have missed out the next-header field. It is needed to start the chain (if there is a chain). And is quite clear in the diagram you quoted.
    There will be one there as well.

    Harry.
     
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  5. kobem

    kobem Megabyte Poster

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    oh my god , we returned to the start ........

    according to you next header is in main header , data will appear after all the headers mean what?

    please i have read lots of documents but
    main header is mentioned version , traffic class , flow label , payload length , hop limit ,source
    ve dest. address " and next header

    and in a document it says "next header consists of payload(data) and extension headers if there is
    ........

    *****************where is data? (it was after dest.address in ipv4 )*********************
     
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  6. BosonMichael
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    BosonMichael Yottabyte Poster

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    No, GBL... he didn't listen to my advice. :popcorn
     
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  7. kobem

    kobem Megabyte Poster

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    i have no other chance , i have to achieve on network field somehow.
    and i am honest about that i am reading so many documents related to ipv6
    though

    i can not understand where payload is in ipv6 , i have no problem with ipv4 but ipv6
    is too complicated
     
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  8. BosonMichael
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    BosonMichael Yottabyte Poster

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    To get into the network field...

    ...start at the bottom...

    ...and work your way up.

    You're trying to work your way into the middle. It simply won't work.

    If you don't have a problem with IPv4, then why are you having such a difficult time figuring out where data goes in a packet?!? :blink IPv6 data goes in the same place as IPv4 data - after the header. Dude - I found this pic in *2* seconds, literally!

    [​IMG]
     
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  9. kobem

    kobem Megabyte Poster

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    that looks nice however from one of my documents i have seen sth like this:

    a-in ipv6 there is a "mandatory main header" then the data thats OK

    b-by means , next header is in main header

    c- main header contains "version, traffic class field , flow label field , hop limit field , source address
    and dest.address field AND NEXT HEADER

    -------1- but extension headers(if any) come after main header ...... if next header is in main header
    how can extension headers come after main header ?----------------

    2- -------but next header includes extension headers (if any) and the protocol and upper layer data-----
     
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  10. kobem

    kobem Megabyte Poster

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    is it like this ?

    [​IMG]
     
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  11. BosonMichael
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    I hesitate to answer this because you don't have the basic foundation of knowledge for most networking topics... and I'm not going to explain each and every part to you in detail - I get paid to do that level of training in the products I create.

    Extension headers, if required, are placed between the IPv6 header and the payload. The Next Header field tells what kind of information is in the next extension header. If multiple extension headers exist, then the first extension header will have a Next Header field that describes what information is in the next extension header. The final extension header in a packet will have a Next Header field that indicates that upper-layer protocol data will follow (for example, a Next Header value of 6 denotes a TCP packet, and a Next Header value of 17 denotes a UDP packet).

    This stuff is easily findable on the Internet - I simply searched for extension headers on Google and clicked on the first link they provided. To be honest, I didn't know anything about extension headers before I wrote this message. But the explanations I found on the Internet were quite clear. It's *really* that easy.
     
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  12. kobem

    kobem Megabyte Poster

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    as i realised from documents , data comes after addresses if no extension headers are avaliable like
    main header + data(payload)

    if we have extension headers , it is main header + extension header + data (payload) shortly
    next header included in main header

    ..........................








    i apprehended them before you replied . Now trying to understand site-local and link-local
    generation only thing i didn't catch that whether link-local and site-local have
    global prefix ? (i mean router)
     
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  13. Sparky
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    Sparky Zettabyte Poster Moderator

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    New year, same posts. Might as well keep drinking! :alc
     
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  14. Luddym

    Luddym Megabyte Poster

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    :biggrin I thought I was in Groundhog day for a minute there.
     
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  15. kobem

    kobem Megabyte Poster

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    hm as i realised

    link - local unicast address is used for hosts on the same link (subnet)
    and it is like below :

    network prefix following interface id

    fe80::/64 (why 64 hence its binary format is 1111(F) 1110(E) 1000(8) 0000(0) then 52 bits zero
    then 64 bits interface id generated by using MAC address)

    site-local unicast address is used for communications on different subnets

    fec0::/48 (it is similar to link-local even though it also has subnet-id(16 bits) then 64 bits interface id)

    ...............................

    "question one" : link-local is for hosts on the same link , due to this
    can we use them in the environment that "shows there are many PCs linked to a switch?"


    "question two" : it seems impossible to use link-local when a router is on but are we able to do the opposite by means using "site-local " also in the example "i have given in question one "?

    "question three" : either site-local or link-local requires a global prefix to complete
    the addressing configuration?
     
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  16. greenbrucelee
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    honestly :cussing:cussing
     
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  17. wizard

    wizard Petabyte Poster

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    [​IMG]
     
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  18. BosonMichael
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    BosonMichael Yottabyte Poster

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    Ah, rather than use different colors and sizes, he's now gone and used different fonts for each question. :rolleyes:
     
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  19. kobem

    kobem Megabyte Poster

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    OK i' m writing down normally !


    "question one" : link-local is for hosts on the same link , due to this
    can we use them in the environment that "shows there are many PCs linked to a switch?"


    "question two" : it seems impossible to use link-local when a router is on but are we able to do the opposite by means using "site-local " also in the example "i have given in question one "?

    "question three" : either site-local or link-local requires a global prefix to complete
    the addressing configuration?
     
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  20. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Not sure exactly what you are asking here - but link-local addresses will be dropped by a router - they are 'unroutable'.

    Yes - but you will need (perhaps) to override the automatic IP address configuration.
    They will have the usual FEx prefixes.

    Harry.
     
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