Engineering / advanced
Addresses, routes, and reachability
Follow packets through addressing, forwarding, routing policy, name resolution, and reachability failures across administrative boundaries.
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Inside this module
Module 01 advanced
Addresses, routes, and reachability
Follow packets through addressing, forwarding, routing policy, name resolution, and reachability failures across administrative boundaries.
- 01
Address space is a hierarchy of bit prefixes
Calculate IPv4 and IPv6 prefix ranges, separate address count from host assignment, and avoid broadcast assumptions that fail across protocols.
22 min - 02
Forwarding chooses the most specific matching prefix
Apply longest-prefix matching to overlapping routes and explain why a more specific blackhole defeats an otherwise healthy aggregate.
21 min - 03
The next hop still needs a reachable link neighbor
Follow IPv4 ARP and IPv6 Neighbor Discovery from route lookup to link-layer delivery, including cache states and first-packet delays.
23 min - 04
Compute paths from topology or neighbor estimates
Compare link-state and distance-vector reasoning, calculate weighted paths, and separate convergence assumptions from transient forwarding behavior.
25 min - 05
BGP chooses permitted paths under administrative policy
Reason about autonomous systems, path attributes, import/export policy, and why a preferred BGP route need not minimize hops or geographic distance.
26 min - 06
Correct final routes can contain unsafe transitions
Construct a routing microloop from asynchronous forwarding updates and measure restoration without confusing hop limits with convergence guarantees.
25 min - 07
Anycast locality is determined by routing
Explain shared service addresses, routing catchments, health-driven advertisements, and the state-continuity risks of anycast path changes.
24 min - 08
Translation capacity is a tuple and state budget
Model network address and port translation with explicit mapping assumptions, distinguish port exhaustion from bandwidth saturation, and account for retained state.
26 min - 09
A negative DNS answer has a type and a lifetime
Follow recursive resolution, distinguish NXDOMAIN from NODATA, and calculate negative-cache lifetimes without confusing DNS TTL with packet hop limits.
25 min - 10
Build a reachability explanation from layered evidence
Investigate names, routes, adjacencies, return paths, and applications while interpreting traceroute responses and packet-size failures cautiously.
28 min