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An Useful Tool of Network Engineers—Ping

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An Useful Tool of Network Engineers—Ping

Besides testing on the terminal, network connectivity testing on the device is also a skill we must have, which is beneficial to check if the configuration we are deploying is as good as we expect. So what else can we do if we test on the device and ping the address directly?

1.Basic operations

Direct ping will send 5 packages. The bottom line is the connectivity test statistics, and “!” Indicates that the package arrived at its destination and returned successfully. If it appears”.” It means timeout, so we need troubleshooting, and there is another common phenomenon that we will talk about later.

2.Ping with source

The source parameter can be used to specify the source address of icmp packages, which helps us to check whether our policies are configured according to our expectations.

3.Modify data

We can use the data parameter to modify the data field in the ICMP package. But it is not commonly used. However, if we need to use the data parameter, we should note that the data value in the Echo Reply package must be the same as that in the Echo package.

4.“Don’t segment”

The df-bit parameter is abbreviation of do not fragment, that is, fragmentation is not allowed. Fragmentation may increase delay and package loss. In addition, the content of the first package after fragmentation is different from that of the subsequent package, which may cause the ACL to identify the abnormal flow of interest. Sometimes we can see the problem through a large ICMP package capture test with fragments.

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5.“Wanning matrix”

Sometimes we need to observe network phenomena for a period of time, perhaps to see whether the route is flipped, to see when the policy takes effect, or simply to test the package loss rate. In this case, we can use the repeat parameter to set the number of packages to be sent. If we want to stop, we can press CTRL+ Shift +6 at any time. Finally, look at the statistics.

6.Modifying package Size

Using the size parameter, you can change the size of ICMP packages at any time. The minimum size is 36 and the maximum size is 18024. Setting it with actual needs.

7.Changing the Timeout Period

In some poor networks, you can modify the timeout parameter to extend the timeout waiting time. The maximum timeout time is 3600 seconds, that is, 1 hour. If a package does not receive a reply within 1 hour, it is estimated that the package will never be received.

8.Mysterious uuuuu

New network workers must have encountered such a problem that at the first time to see you are confused, what is uuuuu? Some who do not know about it may think the switch is broken. In fact, expect “!” “.”, there are many other echo modes on the device. And uuuuu is also common, which refers to “unreachable”. Generally, students who are just beginning to contact with this kind of echo will feel confused, but in fact, this echo is usually caused by policies or routes. Locating the fault is very easy, just traceroute to check which hop is interrupted, and then you can find the fault.

It can be seen that this phenomenon is caused by a policy in R2. Simple trace can quickly locate the fault point. Have you learned it?

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