200-301 official cert guide

200-301 official cert guide.The ping command provides us with the most common network troubleshooting tool. When the ping command succeeds, it determines the IP routing pair 93 Chapter 4, Part 1 Troubleshooting IPv4 Routingmultiple individual parts of the process and troubleshoots some of the possible causes of the problem. When the ping command fails, it usually helps to narrow down the possible causes of the problem and further isolate the problem.This section begins with a short review of how the ping command works. It then provides some suggestions and how to use the ping command to isolate some problems and exclude some items from consideration.Ping Command BasicsThe Ping command tests connectivity by sending a packet to an IP address and expecting a packet back from a device located at that address. ping sends a packet meaning "If you receive this packet, you are in that location and please return a reply to me. "Each time the ping command sends a packet and receives a message back from another host, the ping command can determine that the packet was sent from the source host to the destination and returned.More formally, the ping command uses the Internet Control Message Protocol (ICMP), specifically the ICMP response request and ICMP response reply messages. ICMP can also define many other types of messages, but the two messages listed here are specific to testing connectivity using the ping command. As a protocol, ICMP does not rely on TCP or UDP, and it does not use any application layering protocols. It is simply an IP helper used to help manage IP network functions.For example, Figure 4-6 shows an ICMP message with an IP header, in which a user on host A opens a command prompt and sends the ping172.16.2.101 command to test connectivity to host B. The command sends a response request and waits for a response. The command sends a response request and waits (step ), and Host B receives the message and returns a response answer (step ).172.16.1.51 172.16.2.101 4 IP I ICMP | -------.<--1 IP | ICMP up (I) Zu should answer Figure 4-6 The concept behind the ping 172.16.2.101 command on Host A The ping command is able to gain support from many different devices as well as command operating systems. The command has many options, such as the name or IP address of the destination, the number of times the command sends a response to the request command, the length of time the command waits for a response to be answered (timeout), the size of the packet, and numerous other options. The same command similar in concept to that in Figure 4-6 is used in Example 4-1 to issue the Ping 172.16.2.101 command on Host A.