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Forum Replies

  1. I see.. and the DNS server would obviously be a local DNS server w/ an A record replying w/ a local IP address on the same subnet.

  2. Hi Rene,

    The Ethernet Frame Come to Physical layer then encoded to bit and then bit to signal ??Also please do explain on PRESENTATION LAYER.I can't understand your example .


  3. Hi Zaman,

    That's right. Everything from the data link layer is sent to the physical layer, gets encoded as a signal and is sent on the wire.

    Everything that happens in the application, presentation and session layer is done by the application. That's why for us as network engineers, these layers aren't always very interesting.

    The presentation layer has three roles:

    • Translation: when one person is speaking Chinese and the other English, we won't have much of a conversation. Computers use different character encoding sets like EBCDIC or ASCII. Translation is used to translate from one character encoding set to another.

    • Compression: the presentation layer can do some compression to reduce the data throughput.

    • Encryption: optional but possible, the presentation layer can do encryption. An example is SSL.

    Hope this helps!


  4. Hi,

    I was wondering what can be the issues, if we just dont use the MAC address.
    What if all devices have only IP addresses. What do you think would happen then.

    Here is what I feel:
    1. Every device would have to look up all the way till layer 3 to decide how to forward packets/frames, not just L2.
    2. Using MAC addresses to identify devices on a local network enables us to use any upper layer L3 protocol we want to use, if we used only IP,then we would be stuck with only IP or IPX or AppleTalk etc. We cant use any other way.

    I am not satisfied by my thoughts !
    Can you give some more suggestions ?

  5. @Mansi,
    Without MAC addresses you would have more problems to solve:

    1) Convenience would be a problem. DHCP would no longer be possible, because until you have an IP, you can't communicate on a network. This means that every time you move a computer or device to a new network, you would have to configure it manually.

    2) Management would be a problem. Without setting up a global registry to ensure every IP address is unique from the factory (which would be impossible with IPv4 since there aren't enough addresses), how would you ever be able to track down a mis-configured machine that has a conflicting IP address?

    3) Security would be a problem. How would you stop someone from plugging in a rogue machine to your network and spoofing an IP address without the possibility of layer-2 level security?

    4) Resiliency would be a problem. There are many services, such as GLBP, HSRP, and VRRP, that depend upon a separation of IP addresses from MAC addresses to provide highly available services.

    I am sure there are plenty of other issues that I haven't thought of yet :slight_smile: ...

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