Question

A bridge automatically develops its own “routing table”. It is able to accomplish this through frame forwarding, address learning and loop resolution. Briefly explain each of these three (3) mechanisms.

Any explanation for this question will be really helpful

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Answer 1

Frame Forwarding:

• Keep up forwarding database for each port.

• List station addresses reached through each port.

• Frame arriving on port X:

• Search forwarding database to understand if MAC address is listed for any port excepting X.
• If address not found, forward to all ports except X.
• If address listed for port Y, check port Y for blocking or forwarding state.    Blocking avoids port from receiving or transmitting.If not blocked, transmit frame through port Y.

Address Learning:

• It is also known as backward learning and it can preload forwarding database.
• When frame reaches at port X, it has come from the LAN attached to port X.
• Use the source address to update forwarding database for port X to contain that address.
• If the source address is not establish there, the bridge creates a new entry to the database and timer on each entry in database.
• Each time frame arrives, source address checked against forwarding database.

Spanning Tree Algorithm:

• Address learning mechanism for tree layout it means no closed loops.
• For any connected graph there is a spanning tree that keeps connectivity but contains no closed loops.
• Each bridge assigned unique identifier and exchange among bridges to found spanning tree.