When Packets Vanish
Packet loss is when packets sent never arrive. Even a small loss rate hurts, because TCP treats loss as congestion and slows down, so a lossy link can feel far slower than its raw bandwidth suggests.
Common Causes
Loss comes from a few recurring sources.
- Congestion fills a queue until a router has to drop arriving packets.
- A faulty link or cable corrupts frames so they fail their checksum and are discarded.
- An overloaded host drops packets when its receive buffers fill up.
Each cause leaves different fingerprints, which is why locating the loss matters as much as measuring it.
Narrowing It Down
Use a per hop tool to see where loss first appears and whether it persists to the destination. Check interface counters on your own hosts for drops and errors, since errors point to a physical fault while drops point to overload. Testing at different times can reveal congestion that only appears under peak load.
Key idea
Packet loss makes TCP slow down sharply, and diagnosing it means locating where loss begins and reading the fingerprints, since errors point to a physical fault while drops point to congestion or an overloaded host.