Blog Archives

How to Troubleshoot High Latency with Traceroute Command

High latency in the network can appear due to different reasons, for example congestion in the network, device faults, etc.This is usually measured and referred to as the Round-Trip-Time (RTT) or also Round-Trip-Delay (RTD), which is defined as the time it takes for an Echo message (ping) to reach the destination plus the time for its reply to arrive back to the source.

Two main tools are usually used to measure this network delay: ping and traceroute. While ping returns as output whether a destination is reachable along with statistics about packet loss and RTT, traceroute shows all the hops in the routing path from source to destination along with RTT results for each hop. When troubleshooting high latency issues, it is important to keep in mind the geographical distance between the hops, since longer distances mean longer RTT. As soon as you identify the problematic hops, you can try to ping between them directly and check in the routers in order to find the problem.

For instance, a traceroute can show where in the network (which hop in the routing path) the delay exists or starts. Such an example is shown in the traceroute output below:

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How to Troubleshoot Packet Loss with Ping Command

Packet loss is a common problem in the IP networks. Ping, although simple, is an excellent tool in order to troubleshoot packet loss issues. This post describes how we can detect packet loss in a network using the ping command.

One good way to troubleshoot packet loss issues is to define a large number of ping counts (for example 500) when using the ping command. In this way, it is more possible to catch random packet loss and its pattern will be clearly distinguished by the dots among the exclamation marks. An example of a ping output with packet loss in a Cisco router is shown in the picture below: Continue reading

Using the Ping Command

Ping command is the most common method to check the status of a network entity, the IP connectivity between two nodes or the quality of the network (e.g. delay and packet loss). This post provides an introduction to the ping command and some of its parameters.

With the ping command, the source sends an Internet Control Message Protocol (ICMP) Echo Request to a specific destination address and it returns either a successful ICMP Echo Reply or an ICMP error message (when destination is unreachable). The ping command allows you to define several parameters such as ICMP packet size, number of ping counts, source IP address etc. The ping output differs for different systems.  Continue reading