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data encapsulation question

Discussion in 'Networks' started by kobem, Dec 9, 2007.

  1. kobem

    kobem Megabyte Poster

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    i know this is the basic for networking but all time a question about it
    strolls in my mind

    we say all time ip is connectionless , unreliable , unacknowledged ....

    BUT

    think that a packet will originate from a pc and according to data encapsulation it has to be
    passed all the way down from 7 to 1(layers)

    an email you consider

    7th layer : l7h + data
    6 l6h + l7h + data
    5 l5h + l6h + l7h + data
    4 l4h +l5h + l6h + l7h + data = segment
    3 l3h + ((l4h +l5h + l6h + l7h + data ) = segment)
    2 ...
    1 ....

    so when data passed down to 1 it is sent look at the 3rd layer (l3h + segment)
    and segment includes reliability , end-to-end ....

    so that is ip reliable or not ?
     
    Certifications: CCNA
  2. Sparky
    Highly Decorated Member Award

    Sparky Zettabyte Poster Moderator

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    Yes, it is very reliable. :biggrin
     
    Certifications: MSc MCSE MCSA:M MCSA:S MCITP:EA MCTS(x5) Security+ Network+ A+
    WIP: Exchange 2007\2010
  3. kobem

    kobem Megabyte Poster

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    should the problem be this below

    3th layer : l3h + ((l4h +l5h + l6h + l7h + data ) = segment)

    we mention IP i mean l3h only cause header is about related protocol NOT the network layer ?
     
    Certifications: CCNA
  4. Sparky
    Highly Decorated Member Award

    Sparky Zettabyte Poster Moderator

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    Certifications: MSc MCSE MCSA:M MCSA:S MCITP:EA MCTS(x5) Security+ Network+ A+
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  5. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Depends on your definition of 'reliability'.

    IP is not 'reliable' in the sense that there is no end-to-end checking - that is the reposibility of upper layers.

    That said - the networks that IP usualy sits on are 'reliable', in the sense that usualy any packets get delivered.

    It all depends on what you mean by reliable... :biggrin

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  6. kobem

    kobem Megabyte Poster

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    end-to-end is a big problem man! i suffocate of lots of questions :blink

    1-for ex. NAT mechanism is not counted as end-to-end why not ? maybe cause it changes
    source address (to the hosts those are outside)

    2-but ipsec is end-to-end why ?

    3- also i have read something look at here please : end-to-end connectivity is a property of the internet
    ......................
    however many network elements and techn. do not have this , such as NAT . Without this ,
    each new protocol requires the specific support of network elements it travels through .


    which network elements ? "each new protocol" which ? such as ipsec ?

    4- i asked these yesterday but couldn't understand the answers

    when using NAT/PAT what is the source address that appears to hosts residing outside ?
    (local side of the gateway or public side i mean?)

    same question for ipsec ?

    5-why can't we use ipsec on a NAtted device?
     
    Certifications: CCNA
  7. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Effectively - yes. Many protocols on the 'net assume that both the source and destination IPs are 'real'. NAT breaks that assumption, so breaks many protocols that don't have provision for it.
    IPSec is no different from many other protocols in this regard - it assumes real IPs at each end by default.
    This is saying the same as I am. SIP is another protocol that NAT cause problems with.
    The source IP has to be routable - and will be the IP allocated to the public side of the router.
    For standard IPSec the source IP will be of the device applying the IPSec wrapping.
    You can - if your systems support the extra parts of the protocols.
    See here for the Cisco system. And here for an article from Microsoft on standard work on this.

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  8. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    A brief but useful article on NAT traversal can be found here on Wikipedia.

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+

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