Section 4.2

Question 1

Where in a router is the destination IP address looked up in a forwarding table to determine the appropriate output port to which the datagram should be directed?

Answer 1

At the input port where a packet arrives.

Question 2

Where in a router does “match plus action” happen to determine the appropriate output port to which the arriving datagram should be directed?

Answer 2

At the input port where a packet arrives.

Question 3

Suppose a datagram is switched through the switching fabric and arrives to its appropriate output to find that there are no free buffers. In this case:

Answer 3

The packet will either be dropped or another packet will be removed (lost) from the buffer to make room for this packet, depending on policy. But the packet will definitely not be be sent back to the input port

Question 4

What is meant by Head of the Line (HOL) blocking?

Answer 4

A queued datagram waiting for service at the front of a queue prevents other datagrams in queue from moving forward in the queue.