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IVE GOT TWO QUESTIONS ABOUT NETWORK ?

Discussion in 'Networks' started by kobem, Sep 17, 2007.

  1. kobem

    kobem Megabyte Poster

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    first question is why are we trying to use access control lists or vlans for security
    if we carry "cisco firewall devices" in our network that does the same thing as a hardware?

    second question : according to osi data from a pc or a server , to a pc or a server has a way named encapsulation


    and transport layer is the layer for data transferring

    SO , if transport layer is used for transferring , for example why do we need "http" to transmit and receive web pages , since tcp already gets the job for transfer?
     
    Certifications: CCNA
  2. JonnyMX

    JonnyMX Petabyte Poster

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    Spooky!
     
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  3. ffreeloader

    ffreeloader Terabyte Poster

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    Kobem,

    Do yourself a favor and stop braindumping. Learn fundamentals for a change, and you will be miles ahead.
     
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  4. ThomasMc

    ThomasMc Gigabyte Poster

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    i think you should maybe try and nail down what it is you are trying to achive, as your post seem to be very random at the best of times but heres a good place to get infomation on the diffrence http://en.wikipedia.org/wiki/Http http is the app layer and tcp is the transport
     
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  5. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    TCP may be a transport/session layer entity, but it is a *generic* one. It doesn't know about things like web-pages, usenet news, IRC and the like.

    For that you need applications that communicate using TCP with their own specialized protocols.

    I suggest you get a good book or two on this.

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
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  6. tripwire45
    Honorary Member

    tripwire45 Zettabyte Poster

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    I have to agree with what the others have said thus far, especially Freddy. There are no shortcuts to learning networking. You just have to start with the basics and work your way up.

    You might want to try a book like the Network+ Study Guide or if you don't want to lay out the money to actually purchase a resource, try the following site:

    http://www.learntcpip.com/

    It's free, it's legit, and it will teach you basic networking. Like Freddy said. Leave the braindumps alone. Those sites are full of errors and will do your education more harm than good.
     
    Certifications: A+ and Network+
  7. BosonMichael
    Highly Decorated Member Award

    BosonMichael Yottabyte Poster

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    Looks like I'm already too late for the :popcorn.

    kobem, Freddy's right... stay away from the braindumps, and study legitimately, and you'll start understanding this stuff. But before you can understand it, you HAVE to go back to fundamentals and learn basic networking. I would highly recommend studying for Network+ (and again, stay away from braindumps for it!!).
     
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  8. kobem

    kobem Megabyte Poster

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    hm, you have a nice start man!

    ok , the thing you try to say is tcp and applications(protocols in there)are dependent each other?

    and

    web pages are applications and they have to use their
    own protocols ?

    also think file transfer




    due to encapsulation process , things on source go from seventh layer to first layer then from first to seventh layer on the real destination(not counting routers and switches between source and destination hosts)


    second question : when we mention routers or switches
    we enhance access control lists or vlans but we have firewall devices so i think we do not need acls or vlans ?
     
    Certifications: CCNA
  9. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    The application layer needs something to move the application data - the lower layers do that. Without the lower layers nothing would work.

    Effectively yes. Web pages use HTTP.

    This uses one of FTP, TFTP, SFTP, SCP (and there are others).


    Harry.
     
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  10. kobem

    kobem Megabyte Poster

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    HARRY

    maybe i found the answer

    at application, presentation and session layer : data (pdu)
    at transport layer : source port , destination port , data (protocol information)

    is this true and would the answer be this ?
     
    Certifications: CCNA
  11. Mr.Cheeks

    Mr.Cheeks 1st ever Gold Member! Gold Member

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    How do you know the guy is BD'ing?
     
  12. dmarsh

    dmarsh Terabyte Poster

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    Yes you are kinda correct, its not really the answer though.

    The OSI model is THEORETICAL, whats at each layer will depend on a precise actual situation. TCP is an actual protocol that fits into the transport part of the model. TCP/IP has two parts TCP and IP. Each has a datagram

    http://www.daemon.org/ip.html

    http://www.daemon.org/tcp.html

    The TCP datagram contains the ports, these without the IP addresses from the IP datagram would be useless, see the dependency between the layers ?

    As far as I can see theres no particularly useful distinction between a datagram and a PDU they maybe have some fairly subtle differences. http://www.inetdaemon.com/tutorials/theory/concepts/frames_packets_n_pdus.shtml

    The upper levels presentation, application, session can do whatever they like in reality, they may be only one layer in reality or many layers. They should generally map to the Model in most cases. Application layer will carry application specific data, session will typically not exist in many protocols. Presentation is for encoding data, ASCII / EBCDIC or see CDR etc.

    You need to do a few things to learn :-

    A. Study comms in general, maybe start with basic serial comms, baud, packets, headers/trailers, error correction, compression, encryption etc. Then maybe look at TCP/IP, ARP, RIP etc.
    B. Play with various hardware and software, set up a home router, connect it to your desktop with cat-5, use FTP, HTTP, IRC, Telnet, POP3, SMTP, NNTP, SNMP, whatever other app/protocol you fancy...
    Run network diag stuff, NetStat, Ipconfig, Traceroute, Ping, look into packet sniffers.
     
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