Delivery monitoring—
layout: page
title: Device does not respond suitably to test packets
menu_title: Message 13
weight: 13
navigation:
show: true
nid: 542
mlid: 3394
plid: 3332
breadcrumbs: false
created: 1421430557
—

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.

Recommended action

  1. Verify that the device under test exists and is powered on.
  2. Ensure that ping and traceroute are operational along the test path.
  3. Ensure that appropriate protocols are enabled, i.e. ICMP Echo, ICMP Echo Reply and ICMP TTL Expired messages are enabled along the entire test path.
  4. If it is not possible to enable these protocols, turn on the advanced test setting "Continue test if unable to connect to target". Delivery monitoring will only be able to test the path up to the target, but will not be able to test the target.
  5. Deploy a target monitoring point on the target device to test targets without ICMP Echo connectivity.

Detailed explanation

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 We sometimes see this situation when Internet providers use unpublished addresses in the middle of their network.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.

Possible secondary messages