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arp request or dns request?

Discussion in 'Routing & Switching' started by p1xels, Jul 24, 2013.

  1. p1xels

    p1xels Bit Poster

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    Hi
    This time I am posting a question from Pearsons so it is safe as far as i know & hope people here will not be angry!:oops:

    Here is a diagram from the exam-
    d1.JPG

    I have selected "a" option but I am not sure if its correct. I cant check the answers as the question cant be searched in the accompanying CD! I cant wait either for another time when again I encounter this question in the CD.
    So for the time being I post here for some opinions.
    Hope someone will be kind enough to reply :dry
     
  2. kevicho

    kevicho Gigabyte Poster

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    Interesting question, and i'm not 100% sure the specific answer but id go with D as the machine will be sending its first packet to the default gateway as the WEB server is on a different subnet (The diagram seemingly shows the PC already having the IP address of the Web server in its cache).

    Edit, After another look I cant see any Mac-Addresses on the diagram so im pretty confident now its D)
     
    Last edited: Jul 24, 2013
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  3. danielno8

    danielno8 Gigabyte Poster

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    I can't see what is contained within the exhibit?

    EDIT: Assuming the PC has nothing in either cache however (as i can't see anything):

    ARP for DG MAC address
    Send DNS request to DNS server (with DG MAC as destination mac address)
    Recieve Reply from DNS server
    Send packet to Web server (with DG MAC as destination mac address

    From this if you can see the exhibit you should be able to see what it currently has and get your answer from there.
     
    Last edited: Jul 24, 2013
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  4. p1xels

    p1xels Bit Poster

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    Thank you all
     
  5. paulmarker592

    paulmarker592 New Member

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    I am not sure about it. but D can be used to transfer data at particular gateway.
     
  6. dmarsh

    dmarsh Terabyte Poster

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    From my understanding.

    ARP is a subprotocol of DHCP, it would get used to obtain a dynamic address for a client PC. Its never routed, the route table is built largely from non ARP requests.

    So I'd say B, as you know the default gateway IP address and assuming you already have DNS server address configured.

    My reasoning :-

    1. You don't use ARP to find DNS servers, nor do you identify or route to them by MAC address.
    3. I'm not familiar with IP broadcasts being part of the DNS protocol.
    4. This could work but you already have the IP address for the gateway and you don't need the MAC.
    MAC address gets used as part of ARP until IP address is established. After that you don't need ARP or MAC addresses.
     
    Last edited: Sep 12, 2014
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  7. Sparky
    Highly Decorated Member Award

    Sparky Zettabyte Poster Moderator

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    Was thinking the same thing...
     
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  8. dmarsh

    dmarsh Terabyte Poster

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    You have to be logged in, but I expect there is probably copyright and NDA issues to consider...
     
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  9. danielno8

    danielno8 Gigabyte Poster

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    I think you are misunderstanding ARP somewhat.

    ARP is not a sub protocol of DHCP. ARP is a layer 2 protocol, used to establish the MAC address for a given IP address. Regarding point 4, You always need the MAC of your default gateway, if you want to send any traffic outside your subnet, since you use this MAC address on the destination MAC of any frame which contains a packet destined outside your network.

    SourceIP: You IP
    Destination IP: IP Address of the destination
    Source MAC: You Mac
    Destination MAC: MAC address of default gateway.

    EDIT: I also still can't see the exhibit even while logged in. Just the diagram.
     
    Last edited: Sep 15, 2014
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  10. dmarsh

    dmarsh Terabyte Poster

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    Fair point, seems ARP is used to build frame, must be D then.
     
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  11. danielno8

    danielno8 Gigabyte Poster

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    Can you see the exhibit? I can't see it.....but depending on what is in there, it could also be B (if the PC's ARP table already contains an entry for the MAC address of the default gateway), since if it already has it, there is no need to ARP for it.
     
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