FIT1047 Chap.11 LANs, WANs, Autonomous Systems and CDNs
LANs, WANs, Autonomous Systems and CDNs
LAN and WAN labels describe different local and wide-area scopes, technologies and administrative relationships, while autonomous systems describe coherent external routing-policy domains. One AS can contain many LANs and internal routes. Across the Internet, networks advertise reachability to prefixes and select paths under policy and relationships rather than simple geometric shortest distance.
Exchange points provide shared interconnection infrastructure but do not automatically create universal peering or route-server packet forwarding. Content-distribution networks add application/service selection, edge caches and origin dependencies on top of network routes. A fast nearby response is not automatically a cache hit or authentication claim.
This chapter maps physical, forwarding and administrative views; separates route information from data-plane traffic; and treats CDN selection, cache state, origin contact and user path as distinct evidence. All scenarios are original standard canon within published networking outcomes.
Distributed delivery should be analysed through several aligned but nonidentical maps: physical reachability, prefix forwarding, administrative policy, service selection and cache or origin state. Correlation across regions or dependencies can narrow a fault without proving a hidden routing relationship. An IXP, AS path and CDN edge each answer a different question.
The material is original standard canon for A3's published applied-networking purpose and does not infer the live case, reflection prompt, test mechanics, tools, timing or rubric.
What this chapter covers
- 01
LAN and WAN scope/ownership
- 02
Failure domains and redundancy
- 03
Autonomous-system policy boundaries
- 04
Prefix advertisements and AS paths
- 05
Transit, peering and asymmetric paths
- 06
Internet exchange fabrics and route servers
- 07
CDN selection, edges and origins
- 08
Cache invalidation and distributed observability
- 09
Aligned physical, forwarding and administrative maps
- 10
Separating route information from packet forwarding
- 11
CDN selection, cache and origin evidence
AskSia-authored practice weighting (not an official mark scheme): Fresh regional CDN diagnosis
- localCheck affected users' local path against unrelated healthy services.
- selectionRecord the exact image host, resolved edge and resource rather than testing only the main page.
- edgeCollect edge response timing and cache/origin-contact evidence when authorised.
- pathCompare interdomain path and same resource from an unaffected region.
- conclusionState regional edge/mapping/path hypotheses without selecting one before discriminating evidence.
Key terms
- Autonomous system
- An administrative domain operating a coherent external routing policy for prefixes.
- Transit
- A relationship/service providing reachability beyond an immediate neighbouring network.
- Peering
- An interconnection relationship exchanging defined traffic under participant policy.
- Internet exchange point
- Shared infrastructure where networks can interconnect while retaining independent policy.
- CDN edge
- A distributed service node selected to answer requests closer under network/service policy.
- Origin
- The authoritative upstream source used by a CDN design for content or application state.
- Control plane versus data plane
- The control plane exchanges and selects reachability information, while the data plane forwards packets using installed decisions. Observing an advertised or selected route is not identical to observing the actual request and response path.
- Cache outcome
- The result of an edge's freshness and object-state decision, such as serving stored content or contacting an origin. Edge selection, cache outcome, origin success and user-visible rendering are separate evidence points in a CDN diagnosis.
LANs, WANs, Autonomous Systems and CDNs FAQ
Is an AS the same as a LAN?
No. A LAN is a local link/broadcast environment. One autonomous system can contain many routed LANs and sites under one external policy.
Why is the Internet path not always shortest?
Networks apply commercial, resilience and operational policy to accepted/advertised routes. Return paths can differ because each AS decides independently.
Does joining the same IXP mean two networks peer?
No. The fabric provides interconnection; routing sessions and policy determine whether prefixes are exchanged. A route server can simplify control but usually is not the packet path.
Does a nearby CDN edge guarantee a cache hit?
No. The edge can contact an upper cache or origin, execute logic or serve a hit. Cache metadata or logs are needed.
What makes CDN failure analysis difficult?
Mapping, route, edge, cache, origin and application dependencies change independently and across regions. A shared timeline and exact resource are essential.
Why should an AS relationship not be inferred from one observed path?
A path shows a sequence visible from a particular observation and time, not the complete commercial relationship or all alternatives. Policy, filtering and asymmetry can change selected directions. Relationship labels need explicit scenario evidence.
How should A3 boundaries be stated for Internet and CDN practice?
Use original scenarios to practise the published networking-analysis and reflection purposes. Do not claim the live topology, regional case, test questions, tools, timing or marking format. Those details remain governed by current Moodle instructions.
Assessment move
Draw three aligned maps: physical links/sites, IP prefixes/next hops and administrative AS ownership. Add relationship labels only when the scenario supplies them. Trace route advertisements separately from packet forwarding and allow request/response asymmetry. For IXPs, distinguish shared link fabric, routing sessions/route server and direct participant forwarding.
For CDN questions, record name/selection result, edge identity, cache outcome, origin contact, path and application status. Compare the same object and time across regions to avoid content differences. Analyse common dependencies behind redundant-looking links or distributed edges. Word conclusions proportionally: observed response, selected edge, accepted route and known origin contact are separate claims.
Use the course-developed text to confirm Internet and CDN concepts only. Redraw all topology, policy and delivery maps, and do not copy source prose, figures or examples. Keep relationship labels conditional on supplied evidence, use authorised observations, and confirm A3's actual activities and constraints in Moodle.
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