Distance Vector Routing

No router sees the network. Each one trusts what its neighbours claim — which converges beautifully, until a link fails and bad news has to count its way to infinity.

D(x,y) = min c(x,v) + D_v(y)

∞ = 16 (RIP)

One round per exchange

Network

FixDestination

Animation Speed: 1100ms

Step 1 of 39start · all links up

next hop to Drouting loopD:3advertised to that neighbourchanged this round

Router A

→B1B

→C∞—

→D∞—

Router B

→A1A

→C1C

→D∞—

Router C

→A∞—

→B1B

→D1D

Router D

→A∞—

→B∞—

→C1C

Each row: destination, distance, next hop.

Each router starts knowing only its own links: the cost to each neighbour, ∞ to everyone else. No router has a map. The pink arrows will show each router's next hop towards D.

Rounds to Recover

No fix15 rounds

Poison reverse3 rounds

Same network, same failure, destination D. On the chain poison reverse ends the loop at once; on the triangle the loop runs through three routers and it does not help at all. This is why RIP caps networks at 15 hops — infinity has to be small enough to count to.

Knowledge Check

Question 1 of 3

Routers A–B–C–D sit in a line with cost-1 links, and C–D fails. Without poison reverse, why does it take many rounds for B and C to give up on D?

DSAverse

Distance Vector Routing

Rounds to Recover

Knowledge Check

See also

Distance Vector Routing

Rounds to Recover

Knowledge Check

See also