Tracert / Traceroute - Checking the routes of packets

[Aerosol]

Tracert is a Windows based TCP/IP utility that allows you to determine the route that packets take while traversing through a network to certain destination. It can help You to test intermediate hops and determine possible problems on your network. The same tool can be also found on Linux/Unix like operating systems with slightly changed options - tool is called Traceroute.

It works in a way that increases TTL value "time to live" of each sent packet. When a packet passes through a hop, the hop decrements the TTL value by 1 and forwards the packet to the next hop, so when a packet with a TTL of 0 reaches the next hop, the hop discards the packet with an ICMP "time exceeded" message. By finding out packet hops on the way to it's destination, Tracert can easily help you find routing problems in your network.

Using Tracert to determine route of packets

To any given network destination, there's great possibility that theres more than one route or path for packets to travel to it's destination. After all, this is how internet functions. To determined which route or path, or over which hosts and hops packets are passing through, we can use Tracert (meaning that we're tracing the route).

On Windows, we'll use tracert from command line, going to Start > run > and enter "cmd". We'll trace route from our host 192.168.10.101 to google.com and see over which hops packets are traversing:

C:\Users\John>tracert google.com

 Tracing route to google.com [209.85.148.101]
 over a maximum of 30 hops:

 1     2 ms     2 ms     2 ms  192.168.10.1
 2    36 ms    30 ms    30 ms  85.114.33.42
 3    32 ms    29 ms    30 ms  85.114.32.149
 4    35 ms    35 ms    33 ms  te1-3.ccr01.zag01.atlas.cogentco.com [149.6.30.29]
 5    43 ms    38 ms    41 ms  te1-8.ccr01.vie01.atlas.cogentco.com [130.117.48.77]
 6    49 ms    44 ms    44 ms  te0-1-0-6.ccr22.muc01.atlas.cogentco.com [130.117.1.105]
 7    51 ms    50 ms    49 ms  te0-3-0-2.mpd22.fra03.atlas.cogentco.com [130.117.50.237]
 8   254 ms   266 ms   260 ms  aurora-tel-ltd.demarc.cogentco.com [149.6.140.58]
 9    53 ms    54 ms    52 ms  209.85.241.110
 10   60 ms    55 ms    66 ms  209.85.254.41
 11   51 ms    54 ms    55 ms  fra07s07-in-f101.1e100.net [209.85.148.101]

Trace complete.

From the example, we can see exact point where packets are traversing. Also we see that to reach google.com from our network, traffic has to pass over 11 hops (routers). Result also gives us exact route to our destination. Hovever, Tracert tells us nothing about network latency. To provide network latency and packet loss for each hop (router) and link on the path, We can use tool like Pathping.

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