Understand the Traceroute Command

8/13/2019 Understand the Traceroute Command

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Understand the TracerouteCommandUpdated on July 17, 2013 at 6:26 PM

Introduction A traceroute is a network command that can be run on your computer if you experience routing problems. It traces the hops between your computer and the final destination. For each hop, the traceroute willdiagnose where the problem is.

To Run Traceroute, Follow the Steps Below:

Windows (XP, 2000, 98, or ME)

1. Click Start and then click Run .

2. Type cmd and then click OK .3. Type tracert, the IP address or website name and then click Enter .

Mac OS 10.x

1. Go to the Finder and choose Applications.

2. Select the Network Utility from the Utilities folder.

3. Choose the traceroute tab.

4. Enter an IP address or website name and start the trace.

Gathering and Using Traceroute Information

Follow these guideline s when you run the traceroute command:

Run the command at the time youre experiencing a problem and

compare the results with times when youre not.

Since the Windows tracert command is only a single snapshot of

the network at a point in time, run the command multiple times to

ensure that a fair sampling of data is collected. Post or report the

traceroute that best represents a summary of all of the data youve


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collected.

Copy and paste the command output to a file, as follows:

1. For Windows CMD, right-click in the window, and chose Mark

2. Left-click, hold and drag over the text you want to select.

3. Once the text is fully highlighted, right-click again to copy it into the

clipboard.

4. Move your cursor to the window where you want to pas te it and press

CTRL-v.

If youre having problems with only one particular site or application,

its likely that the issue is localized to the owner of that site or

application. Send your data to the support forums for the site or

application to get resolution.

If the problem isnt limited to a particular site or application, contact

Comcasts Customer Care.

You can do this via Live Chat or by calling 1-800-XFINITY . You can

also post the issue to our web-based support forums .

Reading the Command Output

This is sample output from the Windows tracert command.

Example: tracert Output

H:\>tracert www.example.com

Tracing route to example.com [10.10.242.22]over a maximum of 30 hops:

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12 85 ms 86 ms 84 ms cr2.dlstx.ip.exampleISP2.net[172.30.28.174] 13 84 ms 84 ms 84 ms cr2.la2ca.ip.exampleISP2.net[172.30.28.178] 14 107 ms 84 ms 85 ms gar5.la2ca.ip.exampleISP2.net[172.30.129.25]

15 85 ms 85 ms 85 ms 172.30.255.74 16 85 ms 86 ms 84 ms mdf001c7613r03-gig-10-1.lax1.example.com [10.10.193.242] 17 * * * Request timed out. 18 * * * Request timed out. 19 * * * Request timed out.

NOTES: can be pressed to stop the traceroute. In thisexample, the final *s are due to a firewall blocking traceroute packets. This

is perfectly normal.

The first line of the tracert output describes what the command is doing. Itlists the destination system (example.com), destination IP address(10.10.242.22), and the maximum number of hops that will be used in thetraceroute (30).

The remainder of the output shows information on each hop, which istypically a router, in the path between the sender and the final destination.

Its important to note that the number of hops isnt an important factor thataffects latency. What is most important is the physical distance the packettravels and how it moves between ISPs on the Internet. In this example, thetraffic traverses this route:

1. Starts in Boston and travels toward New York.

2. In New York, it transfers to ISP1.

3. Before leaving New York, it transitions to ISP2.

4. Then it travels south and west through Washington DC, Atlanta, and

Dallas.

5. From Dallas, it travels to Los Angeles.

6. The final destination is Los Angeles where it leaves ISP2 for the end

server.

By car, this distance is well over 3,000 miles, but a fiber path does notalways follow the same path as U.S. interstate highways. The fiber path distance is often further than road miles. Its also important to notethis is only half of the total round trip and the return path could be verydifferent.


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Reading Each Line

Look at Hop 4 below to get familiar with the type of information shown for each hop. It lists the hop number, three measurements for Round TripTime (RTT), the system Name and IP Address reached at that hop.

Example: Hop 4:

Hop RTT1 RTT2 RTT3 Name [IP Address]

4 13 ms 8 ms 9 ms pos-0-3-0-0-cr01.newyork.ny.ibone.comcast.net [68.86.90.57]

Hop number : The specific hop number in the path from the sender to the

destination.

Round Trip Time (RTT): The time it takes for a packet to get to a hop andback, displayed in milliseconds (ms). By default, tracert sends threepackets to each hop, so the output lists three roundtrip times per hop. RTTis sometimes also referred to as latency. An important factor that mayimpact RTT is the physical distance between hops.

If an asterisk (*) appears for RTT, then a packet was not returned within

the expected timeframe.

One or two asterisks for a hop do not necessarily indicate packet

loss at the final destination . Many Internet routers intentionally

discard ping or traceroute packets , but this has no bearing on

applications that use these routers. This practice is called ICMP

Rate Limiting and is used to prevent routers from being impacted by

denial-of-service attacks.Three asterisks followed by the Request timed out message may

appear for several reasons. See the Request timed out Message

sections that follow.

Name : The fully qualified domain name (FQDN) of the system. Many timesthe FQDN may provide an indication of where the hop is physicallylocated. If the Name doesnt appear in the output, the FQDN wasntfound. It isnt necessarily indicative of a problem, if an FQDN isnt found.

IP Address : The Internet Protocol (IP) address of that specific router or host associated with the Name .


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"Request timed out" Message - At the Beginning of a traceroute

A Request timed out message at the beginning of a traceroute is verycommon and can be ignored. This is typically a device that doesntrespond to ICMP or traceroute requests, as shown in Hop 2.

Example Hop 2 :

2 * * * Request timed out.

"Request timed out" Message - At the End of a traceroute

There are several reasons why a Request timed out message mayappear at the end of a traceroute, such as in Hops 17 through 19.

The destinations firewall or other security device is blocking the

request. Even if a firewall is preventing the final hops at the

destination from showing up in traceroute output, the destination is

likely still reachable using the application youre interested in (e.g.

web/HTTP).There could be a problem on the return path from the target system.

Remember the round trip time measures the time it takes for a

packet to travel from your system to a destination system and

back. The forward route and the return route often follow different

paths. If there is a problem on the return route, it may not be evident

in the command output.

There may be a connection problem at that particular system or the

next system.

Example Hops 17 through 19 :

Example Hops 17 Through 19: 17 * * * Request timed out. 18 * * * Request timed out. 19 * * * Request timed out.

Let's Look at the Numbers - Examining Trends

How do you know if the values for RTT are normal or if they indicate a


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potential problem? You need to look at the overall picture depicted in your output.

The following section describes several trends that can occur. As youllsee, a temporary spike may at first glance appear questionable, but mayalso have a perfectly good explanation.

Continue reading to learn how to examine the command output for trends,and help isolate possible issues.

Remember that youre most interested in the destination or final visiblehops in a traceroute. Even if a firewall is preventing the final hops at thedestination from showing up in traceroute output, the destination is likelystill reachable using the application youre interested in (e.g. web/HTTP).

Is the RTT/Latency Acceptable on the Last Visible Destination?

In principle, RTT values of less than 150 ms from your home to the finaldestination shouldnt impact internet applications. Many applications workust fine with latencies even higher than that, but for sites that are US-based they should fall below 150 ms and usually are < 100 ms.

Latency over an uncongested network is primarily dependent on the physical fiber distance between the source (your PC) and the destination(e.g. server). If the source and destination are thousands of miles apart,average latency values of 100-120 ms are acceptable as communicationis limited by the speed of light over the entire physical fiber distance.

Example: Hop 16Hop 16 is the last visible hop in the sample shown previously. The roundtrip times for Hop 16 are acceptable because the round trip times arewithin expected ranges.

16 85 ms 86 ms 84 ms mdf001c7613r03-gig-10-1.lax1.example.com [10.10.193.242]

Do You Notice High Latency on Middle Hops, But Not at the LastVisible Destination?

Traceroute results that show higher latency on middle hops, but not at thelast visible destination do not indicate a network problem . Traceroute

packets can be treated as low priority and may be delayed or dropped,particularly at major public Internet exchanges. The measurement thatsimportant is the last hop or destination .


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Example Hop 5:Hop 5 is a middle hop that shows higher RTTs, possibly because thepackets are being treated as low priority. The packets are flowing throughthe router, however, and the RTTs on the final destination are acceptablefor the distance the packets have traveled (Hop 16).

5 95 ms 100 ms 90 ms xe-10-1-0.edge1.NewYork2.exampleISP1.net [10.1.169.45]

Is There Increased Latency at Middle Hops Which Remains Constantto the Last Visible Destination?

Traceroute results that show increased latency on a middle hop, whichremains similar all the way through to the destination, do not indicate anetwork problem. This can be an artifact of a Multiprotocol Label Switching(MPLS) network.

Example Hop 8:Starting at Hop 8, you can notice that the RTTs jump up to the 84 to 86 msrange. The RTT stays relatively constant to the last visible destination, so aproblem isnt indicated.

6 10 ms 8 ms 9 ms ae-33-89.car3.NewYork1.exampleISP1.net [10.2.16.133] 7 10 ms 9 ms 10 ms 192.205.33.93 8 84 ms 86 ms 84 ms tbr2.n54ny.ip.exampleISP2.net [172.25.3.110] 9 86 ms 86 ms 86 ms cr2.n54ny.ip.exampleISP2.net [172.30.16.133] 10 85 ms 84 ms 85 ms cr2.wswdc.ip.exampleISP2.net [172.30.3.38] 11 84 ms 85 ms 84 ms cr1.attga.ip.exampleISP2.net [172.30.1.173] 12 85 ms 86 ms 84 ms cr2.dlstx.ip.exampleISP2.net [172.30.28.174] 13 84 ms 84 ms 84 ms cr2.la2ca.ip.exampleISP2.net [172.30.28.178]

14 107 ms 84 ms 85 ms gar5.la2ca.ip.exampleISP2.net [172.30.129.25] 15 85 ms 85 ms 85 ms 172.30.255.74 16 85 ms 86 ms 84 ms mdf001c7613r03-gig-10-1.lax1.example.com [10.10.193.242]

Do You See Increasing Latency from the Middle Hop to theDestination?

A traceroute that shows dramatically increased latency on a middle hop,which then increases steadily through to the destination, can indicate apotential network issue. Packet loss or asterisks (*) on many of the middlehops may also indicate a possible network level issue.

This is the type of trend that you will want to report. A steady trend of


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increasing latency is typically an indication of congestion or a problembetween two points in the network and it requires one or more parties tocorrect the problem. We may be able to assist in the reporting of theseissues and sometimes may be able to correct them with the aid of other ISPs.

Example Hops 7 Through 11:The new traceroute output below, illustrates increasing latency from themiddle hop to the destination. Starting at Hop 7, you notice the RTTs jumpup dramatically and that they are out of range. The RTTs for the finaldestination are well over speed of light expectations.

H:\>tracert www.example2.com

Tracing route to example2.com [192.168.32.15]over a maximum of 30 hops:

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Understand the Traceroute Command

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