Cisco CCNA Exam 200-125: Router Tasks when Forwarding Packets

Tasks of a Router when Forwarding Packets

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Question

Which two tasks does a router perform when it receives a packet that is being forwarded from one network to another? (Choose two.)

Answers

Explanations

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A. B. C. D. E.

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When a router receives a packet that needs to be forwarded from one network to another, it performs the following tasks:

  1. Examines the destination IP address: The router examines the destination IP address of the packet to determine the best path for forwarding the packet to its destination. It uses the routing table to determine the next hop or directly connected network to reach the destination.

  2. Removes Layer 2 frame header and trailer: The router removes the Layer 2 frame header and trailer of the incoming packet, leaving only the Layer 3 packet. The Layer 2 information includes the source and destination MAC addresses, as well as the EtherType field.

  3. Encapsulates the Layer 3 packet: The router encapsulates the Layer 3 packet into a new Layer 2 frame with a new source MAC address for the outgoing interface and the destination MAC address of the next hop or the final destination, depending on the routing decision made in the first step.

  4. Forwards the packet: The router then forwards the new Layer 2 frame out of the appropriate interface towards the next hop or the final destination.

Therefore, the correct options are D and A. The router examines the routing table for the best path to the destination IP address and removes the Layer 2 frame header and trailer. Option B is incorrect because the router does not encapsulate the Layer 2 packet. Option C is incorrect because the router does not remove the Layer 3 frame header and trailer. Option E is incorrect because the router does not examine the MAC address table for the forwarding interface.