CompTIA Exam Prep - ITF+, A+, Network+, Security+, CySA+

DiffServ — Differentiated Services — is how quality of service is actually implemented on modern networks. Traffic is marked at the edge, and each device along the path treats it according to that marking. DiffServ versus IntServ The comparison that explains why DiffServ won. IntServ — Integrated Services — reserves resources end to end for each individual flow using RSVP. Every router on the path holds state for every flow. It gives genuine guarantees and it does not scale: a core router carrying millions of flows cannot track them all. DiffServ classifies traffic into a small number of classes, marks each packet, and lets every device apply a per-class behaviour. Routers hold no per-flow state — they read the marking and act. The trade-off is guarantees versus scalability. IntServ promises a specific flow specific resources; DiffServ promises a class relative treatment. DiffServ scales, so DiffServ is what you meet. DSCP and the header The original IPv4 header had a Type of ...

Traffic policing enforces a rate limit by dropping or re-marking traffic that exceeds it. Nothing is buffered and nothing is delayed — traffic either conforms and passes, or it does not and is dealt with immediately. It is the counterpart to traffic shaping, and the exam almost always tests the pair together. This article is about policing specifically. Why drop rather than delay Policing adds no latency, which is its defining advantage. A shaper holds excess traffic in a queue until tokens are available, and that wait is delay and jitter. A policer makes an immediate decision, so conforming traffic passes at line rate with no queuing. That makes policing the right choice when delay is worse than loss, and when you are enforcing a limit on traffic you do not control. The cost is that dropping hurts TCP. Loss triggers retransmission and congestion-window reduction, producing the familiar sawtooth where throughput climbs, hits the limit, collapses and climbs again. Aggressive polici...

Traffic shaping controls the rate at which traffic leaves an interface by buffering packets that exceed a configured rate and releasing them smoothly. It is one half of a pair, and the exam almost always tests it against the other half — policing. Shaping versus policing Both enforce a rate limit. They differ in what happens to the traffic that exceeds it. Aspect Shaping Policing Excess traffic Buffered and sent later Dropped or re-marked Effect on delay Adds latency and jitter No added delay Effect on loss Avoids loss Causes loss Direction Outbound Inbound or outbound Effect on TCP Smooth, fewer retransmits Retransmissions, sawtooth throughput The rule of thumb: shaping delays, policing drops. Shape when you can afford latency but not loss — a file transfer over a metered WAN link. Police when you must not add delay, or when you are enforcing a hard ceiling on someone else's traffic at your network edge. Shaping is outbound only, because you cannot buffer traffic that ...