ccna review book

ccna review book.The Windows command ping is used to check the Layer 3 connectivity between two devices (many devices, including Cisco IOS devices, support the ping feature). The source device sends an ICMP send-back message; if the target device is reachable, it will answer using an ICMP send-back answer message. If the target device is not reachable and there are routers between the source and target devices, the router closest to where the problem occurred will send back the appropriate ICMP message. If that router is on the same network segment as the target device and the target device is unreachable, the router will respond using an ICMP target host unreachable message; if that router does not have a route to the target network, it will respond using an ICMP target network unreachable message.ping uses ICMP sendback messages to initiate tests that check connectivity at the Internet layer (network layer). If the target device is reachable, it will respond using a return answer message for each return message sent by the source device. The WindowsPC commands ping and tracert both check Layer 3 connectivity. ping can be used to check connectivity to devices in the current or other broadcast domains, while traceroute is commonly used to check connectivity to devices in other broadcast domains (across multiple networks).The Windows command ping is executed at the CLI command prompt, and Table 5.5 lists the common options that can be specified there.When troubleshooting a PC, you first need to determine if the user can ping the loopback address: ping 127.0.0.1o If this operation fails, there is a problem with the PC's TCP/IP stack. Next, have the user try pinging the locally configured IP address; if this fails, there is a problem with the PC's IP address configuration. Next, have the user ping the default gateway; if this fails, there is a problem with the configured default gateway address, the default gateway itself, or the subnet mask configured on the user's PC.Table 5.5 Options for the Windows command ping. Option Description-t Sends a continuous sendback request message to the target device; to interrupt the process, use CTRL-C-a Performs reverse name polling, resolving the entered IP address to a fully qualified domain name-n count Sends the specified number of sendback request messages; if this parameter is omitted, 4 sendback request messages will be sent by default-1 size Specifies the length of the sendback request message in bytes: if this parameter is omitted, the default is 32 bytes-f sets the no segmentation (DF) flag in the IP header