Compare distance vector, link state and path vector routing protocols.
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Distance vector routers tell their neighbors which destinations they can reach and at what distance, and believe what neighbors tell them; nobody sees the whole topology. RIP is the classic example, EIGRP an advanced one. Link state routers flood a description of their own links to every router in the area, all build the same map, and each runs SPF (Dijkstra) to compute shortest paths: OSPF and IS-IS. Path vector is BGP: like distance vector, but each route carries the full list of ASes it crossed, which prevents loops and allows policy.
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| Distance vector | Link state | Path vector | |
|---|---|---|---|
| Examples | RIP, EIGRP | OSPF, IS-IS | BGP |
| What is sent | routes and distances | the router's own links (LSAs, LSPs) | routes with AS path and attributes |
| Sent to | directly connected neighbors | flooded to every router in the area | configured peers over TCP 179 |
| View | only what neighbors report | full topology of the area | paths and policy, no topology |
| Algorithm | Bellman-Ford (RIP), DUAL (EIGRP) | SPF (Dijkstra) | best path selection |
| Loop prevention | split horizon, poison reverse, holddown, max hops; DUAL feasibility condition | same database everywhere | own AS in the path means reject |
| Scaling tool | summarization anywhere | areas and levels | aggregation, policy, route reflectors |
Updates and timers
- RIP sends its full table every 30 seconds.
- EIGRP sends partial, bounded updates only when something changes.
- OSPF refreshes each LSA every 30 minutes; IS-IS refreshes LSPs every 15 minutes by default. Both flood changes immediately.
- BGP sends incremental updates and keepalives.
They will ask next
Why is EIGRP called advanced distance vector rather than link state?
EIGRP routers still only learn routes and distances from neighbors and never build a topology map. It adds reliable partial updates, a topology table of neighbor-reported distances, and DUAL, which keeps loop-free backup paths and converges much faster than RIP.
Which converges faster?
Link state protocols and EIGRP converge in well under a second with tuning. RIP can take minutes because of its timers and holddown.
Traps
- Saying link state routers send their whole routing table. They send their links, and each router computes its own table.