How does a router handle an incoming packet whose destination network is missing from the Routing table?

How does a router handle an incoming packet whose destination network is missing from the Routing table?
A. it discards the packet.
B. it broadcasts the packet to each network on the router.
C. it routes the packet to the default route.
D. it broadcasts the packet to each interface on the router.

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13 thoughts on “How does a router handle an incoming packet whose destination network is missing from the Routing table?

  1. For me default route is a part of routing table – If “network is missing from the Routing table” that mine defautl route is not configured.

    A. it discards the packet.

  2. Question says “network is missing from the route table” which include default route. So Answer is A.
    Similar question is there , where the answer is default route… there they do not specify that the network is missing or available in route table

    1. you might be on to something….. the 0/0 in the default route would match the destination network/ip address
      so that be the case…. then the node would black hole the packet….

      i would have to answer it discards the packet

      Paul needs to write the questions for Cisco… 🙂

      just more Cisco confusion….

  3. Poorly written question

    It should read: How does a router handle an incoming packet whose destination network cannot be potentially reached based on the information in the routing table? (meaning there is no default route and no other route)

  4. It depends on the context of the question,
    Had the specified that no other routing configuration made then it would have been safe to assume that the router would discard the packet. But since they haven’t said that we can safely assume a default route was configured, and that the router will transfer the packet across to the next hop specified in the default network.

  5. This is question actually has two possible answers:

    A. it discards the packet.
    – and –
    C. it routes the packet to the default route.

    I guess it also is determined on the context of the question and answer. In this example, only being able to answer with what we are provided and never to assume, the packet would be discarded, assuming from the the question “…destination network is missing from the Routing table…” — meaning that the catch-all network (in best practice)
    0.0.0.0 0.0.0.0 was not configured.

    If 0.0.0.0 0.0.0.0 , the packet would NOT be discarded and the answer C would also satisfy the question.

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