Explain like I'm five · Network

What is a Dynamic Routing Protocol?

RIP/OSPF/IGP, told as a story about post offices trading news and redrawing their map themselves.

old mapto Office Cthe map still says the blocked road is just fine

The road is blocked, but the map hasn't changed.The map still says the blocked road is just fine.

nobody can hand-redraw every road every time something changesmap update pending...A → BB → CC → Droad conditions keep changing — the map can't just sit still

Nobody can hand-redraw the map every time.Road conditions keep changing — the map can't just sit still.

dynamic routing = post offices trade news and redraw the map themselvesRIP by neighbors' rumor, OSPF by sharing the whole map — both are IGPs, rules inside one company

Post offices trade news and redraw the map themselves.RIP fixes the map by neighbors' rumor, OSPF by sharing the whole map — both are IGPs, rules inside one company.

RIP — spreads by rumortells only neighbors, counted in hops
OSPF — shares the whole mapeveryone computes from the same shared map
IGP — the rule inside one orga category of rules used only inside one organization
Self-updatingthe map rewrites itself when a road is cut
RIP — spreads by rumortells only its neighborsjudges by hop countsimple, but news spreads slowlyfits a small networkOSPF — shares the whole mapshares the full map with everyonecomputes shortest path by link statefast news, accurate pathsfits a large network too

RIP and OSPF differ in what they share, how they judge routes, how fast news spreads, and what network size suits them.RIP is simple but spreads news slowly; OSPF is fast and accurate but more complex than RIP.

map news takes a moment to reach every post officeanother company's office needs another rule, like BGP

Map news takes time to spread, and talking to another company needs a different rule.Even with automatic map updates, spreading news takes time — and IGP doesn't reach outside one's own organization.

In one breath

A dynamic routing protocol is a set of rules by which post offices (routers) trade news and update the delivery map (routing table) themselves — RIP, OSPF, and other IGPs.

RIP (Routing Information Protocol) is a distance-vector protocol that propagates hop counts only to neighbors — simple but slow. OSPF (Open Shortest Path First) is a link-state protocol that shares the whole topology map and computes shortest paths — fast and scalable. Both are IGPs (Interior Gateway Protocols) used inside one organization (autonomous system); between organizations, a separate EGP like BGP is used instead.

When grown-ups say it

Dynamic routing
Post offices trading news and redrawing the map themselves. Static routing, by contrast, is redrawn by hand.
RIP
Spreading map news only to neighbors, by rumor. Judges distance by counting hops.
OSPF
Sharing the whole map with everyone. Computes the shortest path from link state.
IGP
A category of routing rules used only inside one organization. RIP and OSPF both belong to this category.
Hop count
The number of post offices a parcel passes through. The yardstick RIP uses to judge a route.
Convergence
All post offices' maps coming to agree. Until then, some maps are still out of date.
IPv6
The far longer new house-address system. The addresses on the routing map itself are moving to this system. → the new, nearly endless address system
DNS
The neighborhood address book. No map helps if the address itself is wrong. → the neighborhood address book
Next story
The Bell That Says a Parcel Just Arrived →
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