The value of tFwdEngDRNeedsICMP indicates the total number of packets dropped by forwarding engine and the received packet requires the router to generate an ICMP message. Some examples include when the IP packet TTL is expired or the destination host, network or Enhanced Subscriber Management (ESM) subscriber is unreachable. Host unreachable can occur, amongst other reasons, if the destination address (e.g. 10.0.1.2) of a packet resolves to a loopback interface subnet (e.g. 10.0.1.1/24) but doesn't match the specific loopback address (e.g. 10.0.1.1). Destination unreachable can also occur, for example, in response to an IPv6 packet received by a router from a point-to-point link (e.g. a non-ethernet link) destined to an address within a subnet assigned to that same link (other than one of the receiving router's own addresses) as described in RFC 4443.