title: Device does not respond suitably to test packets
menu_title: Message 13
There is a device in the path which was detected via the traceroute phase of Delivery monitoring but which does not respond suitably for testing purposes.
The echo reply option may be turned off for this router.
There is another rare routing condition that can cause this symptom. The hop that responded obviously is on the path to the target, and is able to establish a path back to the monitoring point. However, packets that are generated by the monitoring point and that are addressed directly to the discovered hop may not find a path to that device. If this is the case, usually "destination unreachable" messages are returned. We sometimes see this situation when Internet providers use unpublished addresses in the middle of their network.
The "traceroute" phase of Delivery monitoring works by sending packets with low time-to-live (TTL) values in the IP headers. The TTL value specifies how many hops the packet is allowed before it is returned. When a packet can't reach its destination because the TTL value is too low, the last host returns the packet and identifies itself with an ICMP "time exceeded" message. By sending a series of packets and incrementing the TTL value with each successive packet, Delivery monitoring finds out who all the intermediary hosts are. In this case, although the host is there, Delivery monitoring cannot elicit a response from it with subsequent test packets.