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:
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