Alternative connectivity tests

Alternative connectivity tests
4.2.5 This page will introduce some tools that are used to verify basic network connectivity.

Many network protocols support an echo protocol. Echo protocols are used to test if protocol packets are routed. The ping command sends a packet to the destination host and then waits for a reply packet from that host. Results from this echo protocol can help evaluate the path-to-host reliability, delays over the path, and whether the host can be reached or is functional. This is a basic test mechanism. This operation can be performed at either the user or privileged EXEC modes.

In Figure , the ping target 172.16.1.5 responded to all five datagrams that were sent. Each exclamation point (!) indicates a successful echo. Each period (.) on the display indicates that the application on the router timed out while it waited for a packet echo from a target. The ping user EXEC command can be used to diagnose basic network connectivity. The ping command uses Internet Control Message Protocol (ICMP).

The traceroute command, which is often referred to as the trace command in reference materials, can be used to find where data is sent in a network. The traceroute command is similar to the ping command. The main difference is that ping tests end-to-end connectivity and traceroute tests each step along the way. This operation can be performed at either the user or privileged EXEC levels.

In Figure , the path from York to Rome is traced. Along the way the path must go through London and Paris. If one of these routers is unreachable, three asterisks (*) will be returned instead of the name of the router. The traceroute command will attempt to reach the next step until the Ctrl-Shift-6 escape sequence is used.

A basic verification test also focuses on the network layer. Use the show ip route command to see if a routing table entry exists for the target network. This command will be discussed in more detail in a later module of this course.

The procedure to use the ping command is as follows:

• Enter the ping [IP address or name of destination ] command.
• Press the Enter key.

The procedure to use the traceroute command is as follows:

• Enter the traceroute [IP address or name of destination ] command.
• Press the Enter key.

The Lab Activities on this page will allow students to practice three network connectivity tests.

The next page will introduce some tools that are used to troubleshoot IP address-related problems.