Switched Ethernet - Physical vs. Logical Topology

JJBladesterJJBladester MemberMember Posts: 38 ■■□□□□□□□□
I am studying the data link layer. If I have a switch set up to service 10 computers, I believe my physical topology would be a star but the logical topology would be point-to-point. Is this correct?

My reasoning for physical star is because each computer is plugged into a different switch port in a star arrangement. My reasining for a logical point-to-point is that if Computer A wants to talk to Computer B, the switch allows that communication directly as if (logically) Computer A and Computer B were connected point-to-point (like a cable running directly from A to B).

Comments

  • capitanuionutcapitanuionut Member Member Posts: 55 ■■□□□□□□□□
    I am studying the data link layer. If I have a switch set up to service 10 computers, I believe my physical topology would be a star but the logical topology would be point-to-point. Is this correct?

    My reasoning for physical star is because each computer is plugged into a different switch port in a star arrangement. My reasining for a logical point-to-point is that if Computer A wants to talk to Computer B, the switch allows that communication directly as if (logically) Computer A and Computer B were connected point-to-point (like a cable running directly from A to B).

    Physical, a switched Ethernet network is a broadcast multi access network. At the logical level you can say that each device can be identified by the switch by it's mac address, but this after the device sent a message to another device on the network.

    Switches filter frames based on the source mac address of the frame, when it receives on frame it first reads the source MAC address, the writes an entry in the mac-address-table stating that a particular source is on a particular interface. Because the switch doesn't know at the begining where to send the frame, it floods the frame on all ports except the port that it received the frame on (so it's not really a point to point). After all devices are learned the switch will send the frames as a unicast on a particular interface.

    But at this level you need to understand the difference between logical addressing wich occurs at layer 3 ( IP address ) and physical addressing at layer 2 (MAC address). Once you studied all the OSI layers be sure that you understood how a packet goes from a source to a destination (all the encapsulation steps that data goes trough).

    Hope you understood something...i'm quite tired...
  • pham0329pham0329 Senior Member Member Posts: 556
    \My reasining for a logical point-to-point is that if Computer A wants to talk to Computer B, the switch allows that communication directly as if (logically) Computer A and Computer B were connected point-to-point (like a cable running directly from A to B).

    A point-to-point is a connection between 2 devices, and 2 devices only. When you're connecting to a switch, that switch is connected to many more devices so it's not a point-to-point.
  • JJBladesterJJBladester Member Member Posts: 38 ■■□□□□□□□□
    pham0329 wrote: »
    A point-to-point is a connection between 2 devices, and 2 devices only.

    I still think that switches represent logical point-to-point topologies. Per my cisco book, "The logical point-to-point connection between two nodes might not necessarily be between two physical nodes at each end of a single physical link."

    And again, I still think that switches represent star physical topologies.
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