In preparation for your CCNA and CCNP exam success, you’ve got to learn to troubleshoot Cisco routers. And while ping is a great basic IP connectivity tool, it doesn’t give you all the information you need to diagnose network connectivity issues.
Let’s say you have six routers between CityA and CityB. You send a ping from A to B, and get this return:
R1#ping 172.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.1.1.1, timeout is 2 seconds:
…..
Success rate is 0 percent (0/5)
The five periods indicate that there is no IP connectivity to CityB. Problem is, that’s about all ping tells you. You can have 5 or 50 routers between the two points, so how can you tell which downstream router has the problem?
That’s where traceroute comes in. Traceroute sends three datagrams with a Time To Live (TTL) of 1. Those datagrams will timeout once they hit the first router in the path, and that router will respond with an ICMP Time Exceeded message.
In response, the sending router sends three more datagrams, but these have a TTL of 2. This means that the next router in line...
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