PathPing

PathPing

A route tracing tool that combines features of the ping and tracert commands with additional information that neither of those commands provides. The pathping command sends packets to each router on the way to a final destination over a period of time, and then computes results based on the packets returned from each hop. Since pathping shows the degree of packet loss at any given router or link, you can determine which routers or links might be causing network problems.

pathping [-n] [-h maximum_hops] [-g host-list] [-p period] [-q num_queries [-w timeout] [-T] [-R] target_name

Parameters

-n

Does not resolve addresses to host names.

-h maximum_hops

Specifies maximum number of hops to search for the target. Default is 30 hops.

-g host-list

Allows consecutive computers to be separated by intermediate gateways (loose source route) along host-list.

-p period

Specifies number of milliseconds to wait between consecutive pings. Default is 250 milliseconds (1/4 second).

-q num_queries

Specifies number of queries to each computer along the route. Default is 100.

-w timeout

Specifies number of milliseconds to wait for each reply. Default is 3000 milliseconds (3 seconds).

-T

Attaches a layer-2 priority tag (for example, 802.1p) to the ping packets that it sends to each of the network devices along the route. This helps identify network devices that do not have layer-2 priority configured. This parameter must be capitalized.

-R

Checks to see if each network device along the route supports the Resource Reservation Setup Protocol (RSVP), which allows the host computer to reserve a certain amount of bandwidth for a data stream. This parameter must be capitalized.

target_name

Specifies the destination endpoint, identified either by IP address or host name.

PathPing Notes

The pathping command performs the equivalent of a traceroute to identify which routers are on the path. It then sends pings periodically to all of the routers over a given time period, and computes statistics based on the number returned from each.

To avoid congestion, pings should be sent at a sufficiently slow interval.

To minimize the effects of burst losses, do not send pings too close together.

-p period parameter

Pings are sent to each intermediate hop, one at a time. Therefore, the interval between two pings sent to the same hop is (period) x (number of hops).

-w timeout parameter

Multiple pings can be done in parallel, so the amount of time specified in the timeout parameter is not bounded by the amount of time specified for the period parameter for waiting between pings.

-T parameter

Enabling layer-2 priority on the host computer allows packets to be sent with a layer-2 priority tag, which can be used by layer-2 devices to assign a priority to the packet. Legacy devices that do not understand layer-2 priority will toss tagged packets, since they will appear as malformed packets. Therefore, a switch that connects to a legacy network should be configured to strip the tag before forwarding the packets. This option helps identify the network elements that are tossing the tagged packets.

The pathping command is case-sensitive. This parameter must be capitalized.

-R parameter

An RSVP reservation message for a non-existent session is sent to each network device along the route. If the device is not configured to support RSVP, it returns an Internet Control Message Protocol (ICMP) unreachable message. If it is configured to do RSVP, it returns a Reservation Error. Some devices may not return either of these messages. If this happens, pathping returns a timeout message.

The pathping command is case-sensitive. This parameter must be capitalized.

The following example shows output for pathping:

D:\>pathping -n msw

Tracing route to msw [7.54.1.196]
over a maximum of 30 hops:
  0  172.16.87.35
  1  172.16.87.218
  2  192.68.52.1
  3  192.68.80.1
  4  7.54.247.14
  5  7.54.1.196

Computing statistics for 125 seconds...
            Source to Here   This Node/Link
Hop  RTT    Lost/Sent = Pct  Lost/Sent = Pct  Address
  0                                           172.16.87.35
                                0/ 100 =  0%   |
  1   41ms     0/ 100 =  0%     0/ 100 =  0%  172.16.87.218
                               13/ 100 = 13%   |
  2   22ms    16/ 100 = 16%     3/ 100 =  3%  192.68.52.1
                                0/ 100 =  0%   |
  3   24ms    13/ 100 = 13%     0/ 100 =  0%  192.68.80.1
                                0/ 100 =  0%   |
  4   21ms    14/ 100 = 14%     1/ 100 =  1%  7.54.247.14
                                0/ 100 =  0%   |
  5   24ms    13/ 100 = 13%     0/ 100 =  0%  7.54.1.196

Trace complete.

When pathping is run, the first results list the route. This is the same path that is shown using tracert. Next, pathping displays a busy message for approximately the next minute and a half (the exact time varies by the hop count). During this time, pathping gathers information from all the routers previously listed and from the links between them. At the end of this period, it displays the test results.

In the sample report above, the This Node/Link Lost/Sent = Pct and Address columns show that the link between 172.16.87.218 and 192.68.52.1 is dropping 13% of the packets. The routers at hops 2 and 4 also are dropping packets addressed to them, but this loss does not affect their forwarding path.

The loss rates displayed for the links (identified as | in the Address column) indicate link congestion causing the loss of packets being forwarded along the path. The loss rates displayed for routers (identified by their IP addresses) indicate that the CPUs or local packet buffers of those routers might be overloaded.

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