Internet Control Message Protocol (ICMP) messages occur in many situations, such as whenever a datagram...

Internet Control Message Protocol (ICMP) messages occur in many situations, such as whenever a datagram cannot reach the destination or the gateway does not have the buffering capacity to forward a datagram.

Each ICMP message contains three fields: type, code, and checksum. Different types of Internet Control Message Protocols (ICMPs) are identified by a TYPE field.

If the destination is not reachable, which one of the following are generated?