Traceroute explained

Traceroute is a command-line interface based tool used to identify the path used by a packet to reach its target. This tool also uses ICMP messages, but unlike ping, it identifies every router in a path taken by the packets. Traceroute is useful when troubleshooting network problems because it can help identify where exactly the problem is. You can figure out which router in the path to an unreachable target should be examined more closely as the probable cause of the network’s failure.

Traceroute sends a series of ICMP echo request packets to a destination. First series of messages has a Time to Live (TTL) parameter set to 1, which means that the first router in a path will discard the packet and send an ICMP Time Exceeded message. TTL is then increased by one until the destination host is reached and an ICMP echo reply message is received. Originating host can then use received ICMP messages to identify all routers in a path.

NOTE
The traceroute command on Windows is named tracert. On Unix and Cisco IOS traceroute it is invoked using the traceroute command.

 

Here is an example of using the tracert command in Windows:

tracert

In the output above you can see that the traceroute command has listed the IP addresses of all of the routers in the path.

Traceroute on Unix-like operating systems

Traceroute command on Unix works slighty different than the Windows version. It uses UDP packets with a large destination port number (33434 to 33534) that is unlikely to be used by any application at the destination host. Like the Windows version of the command, traceroute on Unix uses TTL to get the IP addresses of the intermediary routers. When a destination host is reached, it replies with an ICMP port unreachable message.

Prerequisites for 200-301

200-301 is a single exam, consisting of about 120 questions. It covers a wide range of topics, such as routing and switching, security, wireless networking, and even some programming concepts. As with other Cisco certifications, you can take it at any of the Pearson VUE certification centers.

The recommended training program that can be taken at a Cisco academy is called Implementing and Administering Cisco Solutions (CCNA). The successful completion of a training course will get you a training badge.

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