We have all heard the same questions at one point in our careers, “Is the Internet down?” or “Getting to X site is slow.” You scramble to a browser to see if Google, ESPN or the NY Times websites are up. Then you fire up traceroute. In some cases, the pages might load slowly, in other cases not at all. These two situations are often downstream fallout of two connectivity issues: latency and packet loss. Latency is the time it takes for a packet to get from source to destination. The speed of light says the latency for one packet to get across the USA from New York to San Francisco is normally between 70-90ms . Packet loss occurs when packets do not make it from their source to destination, being lost along the way. Many factors can contribute to packet loss, including overloaded routers and switches, service interruptions, and human error.
When diagnosing network issues between source and destination, it is helpful to have data to backup your suspicions of slow and inconsistent network performance. Insert Smokeping.