Distance Vector Routing

Tell your neighbours about the world

Examples: RIP, IGRP, EIGRP

• Routers share routing tables with directly connected neighbours
• Each router only knows the distance and next-hop for each destination
• No complete topology knowledge

✅ Simple
✅ Low computation & overhead

❌ Slow convergence
❌ Only works in small networks (max 15 hops for RIP)
❌ Needs split horizon and poison reverse to prevent loops
❌ May not always choose the best path

Link State Routing

Tell the world about your neighbours

Examples: OSPF, IS-IS

• Share what neighbours they are connected (LSAs) to with the world
• Each routed builds a complete topology map (LSDB)
  • All routers will end up with the same LSDB
• Only topology changes are flooded, not full updates

✅ Fast convergence
✅ Loop-free (loop cannot be the shortest path)
✅ Efficient updates, only send changes, not complete state

❌ Complex
❌ Higher resource usage
❌ Needs more planning, i.e. area hierarchy

Path Vector Routing

Similar to distance vector routing, but share all hops instead of just distance

Examples: BGP

✅ Loop prevention: if you see yourself in a path, don't accept the route
✅ Policy control (BGP)
✅ Scalable
✅ Transparency: see full path

❌ Slow convergence
❌ Complex configuration
❌ Needs manual tuning
❌ Large tables
❌ Depends on TCP