We have briefly discussed the check utility in article Interpreting Ping Results-Cisco IOs and Traceroute (Tracert) – Testing the Route, in this article, I am going to give you the short reminder of both ping and tracert utility then we should discuss different issues of inter-VLAN routing in the coming article.
Using the ping command we send an ICMP echo request to the destination address. When a destination host receives an ICMP echo request, it responds with an ICMP echo reply to confirm the ICMP echo request.
It also calculates the time, the echo request was sent and the time the echo reply was received. The time calculation is used to determine the latency of the connection.
If the source of the ping requires successfully receiving a reply from the destination. It confirms that there is a path between the sending device and the receiving device. The figure below illustrates the ping utility. The host 1 is pinging host 2 and the result is showing at the end of the ping test.
Using the tracert utility we can get the complete picture of the hops between source and destination. On UNIX systems, the command has little changes which are traceroute instead of tracert.
The tracert also uses ICMP to determine the path taken with specific time-to-live values defined in the frame. The time-to-live value determines how many hops away the ICMP echo is allowed to reach.
The utility generates the first ICMP echo request with a time-to-live value set to expire at the first hop on the route to the destination device. When the ICMP echo request times get time out on the first hop, an ICMP message is sent back from the first hop to the source device.
The source device records the response from the first hop and sends another ICMP echo request with a greater time-to-live value. This allows the ICMP echo request to pass through the first hop and reach the second devices on route then; it repeats the process until the echo got the final destination device.
When the tracert got the final destination it finishes and displays a list of ingress router interfaces that the ICMP echo request reached on its path to the destination. The figure below illustrates the tracert utility. The host on VLAN 100 is going to trace host 2 on VLAN 200.
The trace is completed, and there are two hops to the destination; the first hop is the fa0/0 the default gateway of VLAN 100, and the other hop is the default gateway of VLAN 200. We can check more hops using this utility, and get the result if there is a problem in any hop.