I have been searching for a answer to this and have not found a definite conclusion. Everything seems to suggest

In what cases may an IP router not forward the packets it receives?

My guess which could be right or wrong is if IP destination address is outside of a LAN or if the IP destination address is not in its routing table.

  • Unfortunately, all "education, certification, or homework" questions are explicitly off-topic here. – Ron Maupin Nov 20 '20 at 20:17

While there may be rules/policies/ACLs explicitly dropping a packet, a router generally cannot forward a packet when it can't be matched to the routing table, ie. when there is not route toward the destination.

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