200-301 official cert guide vol 1

200-301 official cert guide vol 1.Policies and results when performing tests using the ping command Many times, the person who placed the initial problem call from the user (often referred to as a customer support response, CSR) is unable to set up a test from the user4.2 Basics 93 backup to issue the ping command. In some cases, the user is unable to communicate by entering the correct command and right-clicking on the machine, or the user does not exist. As an alternative, a different ping command from a different router can be used to isolate the problem. Tip: For the exam, it helps to practice manipulating ping commands from other routers, which we will discuss later.One problem with using ping commands from other routers (rather than from the host with the problem) is that a single router ping command does not accurately replicate the ping command on the user's device. Nevertheless, each different ping command helps to further isolate the problem. the remainder of the ping command section will discuss how to troubleshoot IPv4 using various ping commands from the router command line interface (CLI). Detecting Longer Routing Problems from Nearby Problem SourcesFor most problems, it will probably begin with the description, "Host X is unable to communicate with host Y." The first troubleshooting step that comes to mind is to issue a ping command from X to Y's IP address. But if the engineer cannot access host X, then the next best thing is to issue a ping command from the router of the closest host to the problem to the IP address of host X.For example, in Figure 4-6, we imagine that a user on host A has called IT support and reported a problem related to sending a packet to host B. The first troubleshooting idea that comes to mind at this point is to send a ping command to the IP address of the nearest host. At this point, the first troubleshooting step that comes to mind would be the ping 172.16.2.101 command for Host A. However, the CSR cannot access Host A or make contact with the user at Host A. Therefore, the CSR remotely logs into Router R1 and issues a ping command to Host B from there, as shown in Example 4-2.Example 4-2 Router R2 issues a ping command to Host B (two commands)Rl# ping 172.16.2.101 Type escapesequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.2.101, timeout is 2 seconds:. !!!! Successrate is 80 percent (4/5), round-trip min/avg/max =1/2/4 ms Rl# ping 172.16.2.101 Type escapesequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.2.101, timeout is 2 seconds: !!!!! Successrate is 100 percent (5/5|, round-trip min/avg/max = 1/2/4 ms)First, take a moment to review the output of the first IOSping command. By default, the Cisco IOSping command sends 5 response (Echo) messages with a timeout of 2 seconds. If the command does not receive a response answer within 2 seconds, then it considers the message to have failed, which is listed as a period. If a response is successfully received within 2 seconds, then the command will display an exclamation point. So, for the first command here, the first response times out, but the other 4 receive matching responses within 2 seconds.The simple explanation is that the example shows a common and normal behavior of the ping command: the first ping command shows a failure, while the rest of the messages are normal. This is often the case because some devices lose ARP table entries in end-to-end routing.