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What is meant by the "match plus action" operation of a router or switch? In the case of destination-based forwarding packet switch, what is matched and what is the action taken? In the case of an SDN, name three fields that can be matched, and three actions that can be taken.

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Match plus action:

Match plus action is nothing but, matching header fields of incoming packet and taking action according to the result.

• In Destination Based forwarding a packet which arrives at a router or a switch is forwarded based on the packets destination address, this forwarding table has two fields.

1. The first field indicates the destination address of the destination host.

2. The second field indicates the path or link interface that has to be opted to reach the destination.

3. In destination based forwarding the first task is to match the arrived packet destination address with the entries in the forwarding table if a match is found proceed further else discard the packet.

4. When a match is found the action attached to the match is executed in order to identify the next hop for the packet.

• In SDN Open Flow forwarding a packet that arrives at a router or switch is forwarded by matching the set fields in the packet with entries in the flow table.

• The fields that are matched are the source IP address, destination IP address, Protocol field, TCP source and destination port fields and many more can are matched with the received packet.

• If a match in the open flow table is found, the actions attached to the entry are executed.

• The most common action usually performed are forwarding the packet, modifying the packet header fields, dropping the packet.

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