What does a traceroute actually show?

+8 votes
We always get asked to run traceroutes and submit them when we have problems. What does a traceroute actually show me?

What exactly are the support agents looking at when then ask for these results?
asked Dec 5, 2014 in ADSL by Zappa (550 points)

2 Answers

+4 votes

traceroute uses a network trick to see how your data travels across the world.  When things are working well, then packets travel quickly, and each hop along the way takes just a little bit longer than the one before it.  When the links are full of other traffic, then getting to the part where you get a reply for the packet you sent takes longer.  

If you read it carefully, traceroute can show you things like:

  • intermittent quality problems
  • link congestion causing latency
  • problems with your home network
  • problems with the telkom ADSL cloud
  • problems with local and international connectivity
  • problems afecting one network and not another

For home networks, your first hop should be really quick (under 1 millisecond for LAN, under 4ms for wireless).  The second hop over ADSL is generally 20 to 40 ms of additional lag (latency).  If your line is busy, this can go really high (e.g. 500ms) which is a sign that your line is too busy.  When there are little stars around, it says that you are losing packets, or the routers are feeling grumpy (it's a bit hard to tell reliably).  When the latency changes wildly it means that things are not stable - lots of traffic, or noise that comes and goes. 

Here's a traceroute to the google DNS:

traceroute 8.8.8.8
traceroute to 8.8.8.8 (8.8.8.8), 30 hops max, 60 byte packets
 1  192.168.0.1 (192.168.0.1)  1.158 ms  1.599 ms  1.972 ms A little slow on the first hop
 2  105-236-7-1-esr-lo.mtnbusiness.co.za (105.236.7.1)  9.756 ms  10.988 ms  13.381 ms  All the way to Telkom this line is a bit inconsistent
 3  ipc-recieve-jh-1a.za.mtnbusiness.net (41.181.178.5)  17.615 ms  19.736 ms  23.464 ms  All the way to MTN
 4  qux-jh-dca-2.za-b.za.mtnbusiness.net (41.181.165.115)  26.208 ms  28.066 ms  30.278 ms
 5  jh-dca-2.za--qux-b.za.mtnbusiness.net (41.181.165.114)  33.551 ms  35.915 ms  38.366 ms
 6  41.181.180.10 (41.181.180.10)  238.811 ms  207.155 ms  207.150 ms  Leaving the country - extra latency
 7  ls-cr-2.uk--rb-cr-1.za-g.mtnns.net (196.44.31.114)  209.594 ms  211.694 ms  213.903 ms
 8  ls-pr-2.uk--ls-cr-2.uk-a.mtn.net (209.212.111.187)  216.780 ms  219.228 ms  205.537 ms
 9  google-peering-ls-pr-2.uk.mtnns.net (209.212.99.13)  207.307 ms  209.868 ms  212.013 ms
10  209.85.255.78 (209.85.255.78)  232.096 ms 209.85.255.76 (209.85.255.76)  225.442 ms 209.85.255.78 (209.85.255.78)  236.625 ms
11  209.85.245.2 (209.85.245.2)  239.688 ms 216.239.51.3 (216.239.51.3)  224.907 ms proxy.google.com (216.239.51.5)  245.023 ms
12  64.233.174.82 (64.233.174.82)  196.516 ms  197.207 ms 72.14.242.166 (72.14.242.166)  201.456 ms
13  216.239.51.151 (216.239.51.151)  212.336 ms 72.14.239.98 (72.14.239.98)  212.687 ms  215.027 ms
14  * * *  Grumpy router doesn't respond
15  google-public-dns-a.google.com (8.8.8.8)  208.873 ms  211.216 ms  214.185 ms

 

In windows, traceroute is called tracert

answered Dec 5, 2014 by Bananaman (5,390 points)
+1 vote

There are three main primary objectives of traceroute tool. These objectives fulfilled by tracroute gives an insight to your network problem.

 

  1. The entire path that a packet travels through

  2. Names and identity of routers and devices in your path

  3. Network Latency or more specifically the time taken to send and receive data to each devices on the path

 

If you looking at the actual traceroute, you looking at timeout's (represented as "*"), millisecond response time and the path/hop to identify where the fault is

answered Dec 5, 2014 by Matthew Murdoch (61,380 points)
...