Troubleshooting a Simple Network Flashcards
During operation, network devices generate messages about different events. These messages are sent to an operating system process. This process is responsible for sending these messages to various destinations, as directed by the device configuration. Logging messages are also sent to the console by default. Even if the global logging process is disabled, logging messages are nevertheless sent to the console. You can decide about the severity level of the logged messages and their destination.
Logging
(ICMP) is a supporting protocol in the TCP/IP protocol suite. It is used by network devices, including routers, to send error messages and operational information indicating, for example, that a requested service is not available or that a host or router could not be reached.
Internet Control Message Protocol (ICMP)
A successful ping to an IPv4 address means that the endpoints have basic IPv4 connectivity between them.
ping
The results of traceroute to an IPv4 address can help you determine how far along the path data can successfully reach.
traceroute (or Microsoft Windows tracert)
Used to test the transport layer connectivity for any TCP port over IPv4.
Telnet or SSH
Used to display the mapping of IPv4 addresses to media access control (MAC) addresses to verify connected devices.
show ip arp or show arp (or Microsoft Windows arp -a)
Used to display the IPv4 address configuration of the interfaces.
show ip interface brief (or Microsoft Windows ipconfig /all
Access the command prompt and ping 127.0.0.1. This address is the diagnostic or loopback address. If you get a successful ping, your IPv4 stack is considered to be initialized. If it fails, you have an IPv4 stack failure, and you need to reinstall TCP/IP on the host.
Ping the Loopback Address
From the command prompt, ping the IPv4 address of the local host. If the ping is successful, your network interface card (NIC) is functioning. If it fails, there is a problem with the NIC. If the ping is successful, it does not mean that a cable is plugged into the NIC, but only that the IPv4 protocol stack on the host can communicate to the NIC (via the LAN driver).
Ping the IPv4 Address of the Local Interface
From the command prompt, ping the default gateway (router). If the ping works, it means that the NIC is plugged into the network and can communicate on the local network. If it fails, you have a local physical network problem that could be anywhere from the NIC to the router.
Ping the Default Gateway
If the previous steps are successful, try to ping the remote server. If the ping is successful, then you know that you have IPv4 connectivity between the local host and the remote server. You also know that the remote physical network is working.
Ping the Remote Server
If the previous steps are unsuccessful, there may be an incorrect default gateway configuration on either the host or the server, or there may be a routing issue.
You can use the traceroute utility to test the path that packets take through the network, to ensure that they are going through the router.
Check the Default Gateway
