Cisco Show Commands Ping and Tracert Basic commands

Cisco Show Commands Ping and Tracert Basic commands 

In this post you will learn some Cisco Basic commands including Cisco Show Commands, Ping and Tracert commands. At the end of this topic you will several commands to monitor and maintain network connectivity. To test network connectivity to local and remote destinations, commands such as ping , telnet and traceroute are often used . On Cisco IOS devices, the show version command can be used to verify and troubleshoot some of the basic hardware and software components. To view information of all network interfaces on a router, the show ip interface command is used .
Ping and tracert commands are used to establish the relative performance of the network. And the basic show commands to verify the configuration and status of a device interface and use the basic commands of the host and IOS to obtain information about the devices in a network.
Once the network is implemented, the administrator should be able to test the network connectivity to make sure it works correctly. In addition, it is recommended that the network administrator perform a network registration.

THE PING COMMAND

The ping command is an effective way to test connectivity. Generally, this test is known as the " protocol stack test ", because the ping command goes from layer 3 of the OSI model to layer 2 and then to layer 1. This command uses the ICMP protocol to verify connectivity. The ping command does not always identify the nature of a problem, but it can help identify its origin, an important first step in troubleshooting a network failure.
The ping command provides a method to test the protocol stack and IPv4 address configuration on a host, as well as to test connectivity to local or remote destination hosts, as shown in the illustration.

IOS PING INDICATORS

A ping emitted from the IOS results in one of several indications for each ICMP echo sent. The most common indicators are:

• ! (exclamation point): indicates the reception of an ICMP echo response message. Indicates that the ping completed successfully and verifies layer 3 connectivity.
• . (period): Indicates that the time was up while waiting for an ICMP echo response message. May indicate communication problems. You can point out that there was a connectivity problem somewhere along the route. It can also indicate that a route router did not have a route to the destination and did not send an ICMP message of unreachable destination. You can also point out that the ping was blocked by device security.
• U : An unreachable ICMP message was received. Indicates that a router on the route did not have a route to the destination address or that the ping request was blocked and responded with an ICMP message of unreachable destination.

LOOPBACK TEST

The ping command is used to verify the internal IP configuration on the local host. Remember that this test is performed using the ping command at a reserved address called " loopback address " (127.0.0.1). This verifies that the protocol stack works correctly from the network layer to the physical layer and vice versa, without actually placing a signal in the media.
Ping commands are entered on a command line. Use the following syntax to ping the loopback address:

EXTENDED PING

Cisco IOS offers an "extended" mode of the ping command .
This mode is entered by typing " ping " (without the quotes) in the privileged EXEC mode, without a destination IP address. Then, a series of input requests is presented, as shown in the following example. Pressing Enter accepts the indicated default values.

The following example shows how to force the source address for a ping to be 10.1.1.1 (see R2 in the illustration); the source address for a standard ping would be 209.165.200.226. In this way, the network administrator can verify remotely (from R2) that R1 has route 10.1.1.0/24 in its routing table.

By entering a longer timeout period than the default, possible latency problems can be detected. If the ping test is successful with a higher value, there is a connection between the hosts, but there may be a latency problem in the network.

INTERPRETATION OF TRACERT MESSAGES

A trace provides a list of hops when a packet is routed through a network. The form of the command depends on where the command is issued. When you perform the scan from a Windows computer, use tracert . When tracking from a router's CLI, use traceroute .

Here, on the basis that the command is issued from a Windows computer, the tracert form is used:

The only correct answer was that of router A's gateway. The timeout for trace requests timed out, which means that the next hop router did not respond. The results of the trace command indicate that the fault is then in the internetwork beyond the LAN.

Cisco SHOW COMMANDS

The Cisco IOS CLI show commands show important information about device configuration and operation. Network technicians use show commands frequently to view configuration files, check the status of processes and device interfaces, and verify the device's operating status. The show commands are available regardless of whether the device was configured using the CLI or Cisco Configuration Professional.
You can display the status of almost all router processes or functions using a show command. Some of the best known show commands are:
show running-config
show interfaces
show arp
show ip route
show protocols
show version

VIEW ROUTER CONFIGURATION USING THE SHOW VERSION COMMAND

Once the boot configuration file is loaded and the router boots correctly, the show version command can be used to verify and resolve the problems of some of the basic hardware and software components used during the boot process.

The result of the show version command includes the following:

• The version of the Cisco IOS software that is being used.
• The bootstrap software version of the system stored in the ROM that was initially used to boot the router.
• The full filename of the Cisco IOS image and where the bootstrap program placed it.
• The type of router CPU and the amount of RAM. It may be necessary to update the amount of RAM when updating Cisco IOS software.
• The quantity and type of physical interfaces of the router.
• The amount of NVRAM. The NVRAM is used to store the startup-config file.
• The amount of router flash memory. It may be necessary to update the amount of flash when updating Cisco IOS software.
• The currently configured value of the software configuration register in hexadecimal format.

The configuration log tells the router how to start. There are several possible configurations for the configuration register. The most common are the following:

• 0x2102 : factory default settings for Cisco routers (load the IOS image from flash memory and boot configuration file from NVRAM).
• 0x2142 : The router ignores the content of nonvolatile RAM (NVRAM).

On a switch, the show version command displays information about the currently loaded software version, along with hardware and device information.

Some of the data shown by this command are the following:

• Software version: IOS software version.
• Bootstrap version: bootstrap version.
• System activity time: time elapsed since the last time it was restarted.
• System restart information : restart method (for example, off and on, collapse).
• Software image name: IOS file name.
• Switch platform and processor type : model number and processor type.
• Memory type (shared / main) : Main processor RAM and shared packet I / O buffering.
• Hardware interfaces: interfaces available on the switch.
• Configuration log : sets boot specifications, console speed settings and related parameters.

HOST AND IOS COMMANDS

The IP address of the default gateway of a host can be seen by issuing the ipconfig command on the command line of a Windows computer.

A tool to analyze the MAC address of a PC is ipconfig / all . Note that, the PC's MAC address now appears along with several details related to the layer 3 addressing of the device. Try using this command.

In addition, the manufacturer of the network interface on the PC can be identified by the OUI portion of the MAC address. This can be investigated on the Internet. The DNS client service on Windows PCs optimizes the performance of DNS name resolution by previously storing resolved names in memory. The ipconfig / displaydns command shows all DNS entries in cache on a Windows computer system.

ARP COMMAND OPTIONS

The arp command allows you to create, edit and display physical address assignments to known IPv4 addresses. This command is executed from the Windows command prompt.

To execute an arp command, enter the following at a host prompt:

C: \ host1> arp -a

The arp -a command lists all the devices that are currently in the host's ARP cache, which includes the IPv4 address, physical address and type of addressing (static / dynamic) for each device.

SHOW CDP NEIGHBORS COMMAND OPTIONS

Examine the result of the show cdp neighbors commands , with the topology of Image 10. Note that R3 has collected detailed information about R2 and the switch connected to the R3 Fast Ethernet interface.

CDP is a Cisco-exclusive protocol that runs on the data link layer. Because the CDP protocol works at the data link layer, it is possible for two or more Cisco network devices to obtain information from each other even if there is no Layer 3 connectivity. In network detection situations, the neighbor's IP address with CDP is usually the only information needed to connect to that device via Telnet. For obvious reasons, CDP can pose a security risk. Because some versions of IOS send CDP publications by default, it is important that you know how to disable CDP.

SHOW IP INTERFACE BRIEF COMMAND

In the same way that commands and utilities are used to verify the configuration of a host, the commands can be used to verify the interfaces of intermediary devices.

ROUTER INTERFACE VERIFICATION

One of the most used commands is the show ip interface brief command . This command provides a shorter result than the show ip interface command . Provides a summary of the key information for all the network interfaces of a router.

The result of show ip interface brief shows all the router interfaces, the IP address assigned to each interface (if any) and the operating status of the interface. Depending on the result, the FastEthernet0 / 0 interface has the IP address 192.168.254.254. In the last two columns of this line, the status of layer 1 and layer 2 of this interface is shown. The up (active) value in the Status column shows that that interface operates at layer 1. The up value in the Protocol column indicates that the layer 2 protocol works. Also note that the Serial 0/0/1 interface was not enabled. This is indicated by the administratively down value in the Status column. As with any final device, it is possible to verify layer 3 connectivity with the ping and traceroute commands. In this example, both the ping command and the trace command show satisfactory connectivity.

VERIFICATION OF SWITCH INTERFACES

The show ip interface brief command can also be used to verify the status of the switch interfaces. The IP address for the switch is applied to a VLAN interface. In this case, the Vlan1 interface received the IP address 192.168.254.250 and is enabled and running.
The result also shows that the FastEthernet0 / 1 interface is inactive. This indicates that there is no device connected to the interface or that the device that is connected to it has a network interface that does not work.

On the other hand, the result shows that the FastEthernet0 / 2 and FastEthernet0 / 3 interfaces work. This is indicated by the up value in the Status and Protocol columns.

Layer 3 connectivity on the switch can also be tested with the show ip interface brief and traceroute commands . In this example, both commands show satisfactory connectivity.

It is important to note that no IP address is required for a switch to fulfill its function of frame forwarding at layer 2. An IP address is required only if the switch is managed over the network via Telnet or SSH.