Detecting sources of computer network failures

A method comprising:

• identifying a particular path of a network flow in a computer network between a source and a destination, wherein the particular path comprises one or more network devices coupled by one or more links;
• and
• in response to a determination that there is no end-to-end connectivity between the source and the destination along the particular path, determining whether a network component of the particular path in the network flow has failed comprising:
• requesting that the destination transmit a respective trace diagnostic packet to each network device along the particular path, wherein each trace diagnostic packet is configured to follow the particular path and has a particular value in a time-to-live field configured to cause a corresponding network device to send at least a time exceeded message in response to that trace diagnostic packet, wherein the time exceeded message includes a portion of the trace diagnostic packet that includes a packet identifier inserted into a first plurality of bits of the trace diagnostic packet;
• and
• determining whether at least one network component that is part of the particular path of the network flow has failed based on results of the trace diagnostic packets.

A system comprising:

• one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising:
• identifying a particular path of a network flow in a computer network between a source and a destination, wherein the particular path comprises one or more network devices coupled by one or more links;
• and
• in response to a determination that there is no end-to-end connectivity between the source and the destination along the particular path, determining whether a network component of the particular path in the network flow has failed comprising:
• requesting that the destination transmit a respective trace diagnostic packet to each network device along the particular path, wherein each trace diagnostic packet is configured to follow the particular path and has a particular value in a time-to-live field configured to cause a corresponding network device to send at least a time exceeded message in response to that trace diagnostic packet, wherein the time exceeded message includes a portion of the trace diagnostic packet that includes a packet identifier inserted into a first plurality of bits of the trace diagnostic packet;
• and
• determining whether at least one network component that is part of the particular path of the network flow has failed based on results of the trace diagnostic packets.

One or more non-transitory computer storage media encoded with computer program instructions that when executed by one or more computers cause the one or more computers to perform operations comprising:

• identifying a particular path of a network flow in a computer network between a source and a destination, wherein the particular path comprises one or more network devices coupled by one or more links;
• and
• in response to a determination that there is no end-to-end connectivity between the source and the destination along the particular path, determining whether a network component of the particular path in the network flow has failed comprising:
• requesting that the destination transmit a respective trace diagnostic packet to each network device along the particular path, wherein each trace diagnostic packet is configured to follow the particular path and has a particular value in a time-to-live field configured to cause a corresponding network device to send at least a time exceeded message in response to that trace diagnostic packet, wherein the time exceeded message includes a portion of the trace diagnostic packet that includes a packet identifier inserted into a first plurality of bits of the trace diagnostic packet;
• and
• determining whether at least one network component that is part of the particular path of the network flow has failed based on results of the trace diagnostic packets.