Given the network of switches and nodes shown in the figure below. Consider that

Question

Given the network of switches and nodes shown in the figure below. Consider that Switches S1 and S2 has four interfaces numbered 1,2,3 and 4, while S4 has two interfaces numbered 1 and 2 74-29-9C-E8-FF-55 1A-23-F9-CD-06-9B Where A's MAC address is:74-29-9C-E8-FF-55 and H's MAC address is: 1A-23-F9-CD-06-9B Given the information above, consider A sends a frame to H and H responds back with a frame to A. The switching tables at S1 would be? a. S1 table Node A:74-29-9C-E8-FF-55 H:1A-23-F9-CD-06-9B Interface 4 b. S1 table Node A:74-29-9C-E8-FF-55 H:1A-23-F9-CD-06-9B Interface C. S1 table Node A:74-29-9C-E8-FF-55 H:1A-23-F9-CD-06-9B Interface d. S1 table Node A:74-29-9C-E8-FF-55 H:1A-23-F9-CD-06-9B Interface

Explanation / Answer

Right option is A).

A send a frame to H.

Initially the switching table is empty.

When a frame with its source and destination MAC arrives to switch S1.S1 stores it and check the frame for its destination.but since its table is empty it doesn't know where the switch is supposed to send the frame.but since,the frame came from interface 1 it does know MAC address of host attached to interface 1.it updates its table with MAC address of A with interface 1.

Now,since it doesn't know where the destination in reality.so,it send that frame to all the interfaces through which they are connected to other host except interface 1.due to this from interface 4 it goes to switch S4.S4 update its table with MAC address of A and its interface 1.but it doesn't know where the destination is? it sends the frame to all its other interfaces.due to this the frame from interface 2 of switch S4 reaches S2 through its interface 4.

Switch S2 check the frame for source and destination MAC and update its table for Mac Address of host A and interface 4.but it doesn't know where the destination is?so, it sends the frame to all other interfaces.all the host to which frame doesn't belong to discards the frame and the host to which frame actually belongs to accept it and send the respond back to host A.

This response is first intercepted by S2.S2 now knows hows to send frame to its destination.but from the response frame it checks source address and update it table with MAC address of host H and interface 2.now,since S2 knows the path to A it senda the frame only to interface 4.

From interface 4 of S2 it reaches S4.S4 checks the response frame and update it table with MAC address of host H and interface 2.Since,S4 knows the path to S1 it sends the frame to only that interface through which it can reach host A.i.e to interface 1.

from interface 1 of switch S4 it reaches S1.S1 checks the response frame and update its table with MAC address of H and interface 4.S1 sends the frame to its destination A through interface 1 because its table has entry for it.

So,right option is Option A).

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