Know the protocol. Debug the system.
You can recite the TCP state machine. But when 2% packet loss silently collapses HTTP/2 throughput across every stream, that model stops helping. zerohop's kernel-validated simulators show the cross-layer cascade — so you trace it, not guess it.
Cascade computed server-side · drag the slider to recompute
Most protocol knowledge is declarative — you can name the states and cite the RFC. Debugging demands something else: a causal model of how a change in one layer forces the next to react. That gap is why a transport-layer failure can burn hours looking like an application bug. zerohop builds that model by making the cascade visible one parameter at a time, then tests your judgment against what the kernel actually does.
See parameters change in real time
Drag a slider and watch the simulation respond instantly — packet loss, RTT, window size, hold timers. No replays, no canned scenarios.
Watch the cascade across layers
A server-side correlation engine computes how one component's state ripples into the next, so you see the failure propagate — not just the symptom.
Build judgment with katas
Predict the outcome, observe what actually happens, then reflect on the gap. Repetition turns protocol facts into debugging instinct.
Available modules
TCP Connection Lifecycle
net/ipv4/tcp_input.c
Trace why 2% packet loss collapses throughput across every HTTP/2 stream.
BGP Session Lifecycle
bgpd/bgp_fsm.c
Read the FSM well enough to know why a session is stuck in Active, not Established.
Validated against:
- Linux kernel v6.12.93
- FRRouting frr-10.6.1