Net Tip: Using pathping

Friday Feb 1st 2002 by Jim Freund

The pathping command is a relatively obscure, yet simple and powerful tool for tracing network problems; one-upping its antecedants ping and tracert. Learn how to use it within this article.

More often than not, knowing that there are connectivity problems between two computers is not enough information to effect a fix. You can use the ping command, which will send four ICMP echo packets to the target, and then listens for the replies on the originating machine. The tracert command displays the Fully Qualified Domain Name and IP address of each gateway along the route to a remote computer. Together, you can glean a little information about what's going on, but you're probably still in the dark as to exactly where the problem lies.

Shedding more light on the issue is pathping; a relatively obscure, yet simple and powerful command in the Windows NT/2K/XP arsenal. Basically a hybrid of ping and tracert, pathping one-ups these traditional utilities by providing statistical analysis of results over a period of time -- usually about 5 minutes. (This can vary dependant on the number of hops being analyzed enroute.) In addition to returning the computer name and IP address for each hop, pathping computes the percentage of lost/sent packets to each router or link. This additional information is what enables you to isolate the cause of a network problem.

Syntax: pathping [-n] [-h maximum_hops] [-g host-list] [-p period] [-q num_queries] [-w timeout] [-t] [-R] [-r] target_name

-n Do not resolve IP addresses to hostnames.
-h maximum_hops Maximum number of hops to search for target. Default is 30
-g host-list Allows loose source route along host-list. (consecutive computers to be separated by intermediate gateways)
-p period Wait period milliseconds between pings. 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). It is suggested you don't go below the default number, so as to avoid network congestion.
-q num_queries Number of queries per hop. Default is 100
-w timeout Wait timeout milliseconds for each reply. Default is 3000 milliseconds. 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 Test connectivity to each hop with Layer-2 priority tags. This parameter 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.

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.

-R Test if each hop is Resource Reservation Setup Protocol (RSVP) aware, which allows the host computer to reserve a certain amount of bandwidth for a data stream. This parameter must be capitalized.

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.

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