Distance Vector vs Path Vector Protocols | Generated by AI
Question: What are distance-vector and path-vector routing protocols? What is the difference between them, especially since path-vector is described as an advanced form of distance-vector?
Answer:
Distance-vector and path-vector are two classes of dynamic routing protocols used in computer networks to determine the best paths for forwarding packets.
Distance-Vector Routing Protocols
- Routers exchange vectors (lists) of known destinations along with a distance metric (e.g., hop count or composite metric) to each destination.
- Each router shares its entire routing table periodically with directly connected neighbors.
- Routers do not have knowledge of the full path—only the distance and the next-hop neighbor.
- They use algorithms like Bellman-Ford to compute the lowest-cost path.
- Common issues: Susceptible to routing loops and the “count-to-infinity” problem (mitigated by techniques like split horizon and poison reverse).
- Examples: RIP (Routing Information Protocol), IGRP.
- Typically used in smaller, intra-domain (interior gateway) environments.
Path-Vector Routing Protocols
- An enhanced or advanced variant of distance-vector, specifically designed for large-scale, inter-domain routing.
- Routers exchange not only a metric (often AS path length) but also the full path (sequence of autonomous systems or nodes traversed).
- This path information is appended as routes are advertised, allowing easy detection and prevention of loops (if a router sees its own identifier in the path, it discards the route).
- Supports complex policy-based routing (e.g., preferring certain paths for business or security reasons).
- Primary example: BGP (Border Gateway Protocol), the protocol that glues the Internet together by routing between autonomous systems (ASes).
- No periodic full table updates like classic distance-vector; updates are incremental and triggered.
Key Differences
| Aspect | Distance-Vector | Path-Vector |
|---|---|---|
| Information Shared | Distance/metric + next hop | Full path (e.g., AS sequence) + metric |
| Loop Prevention | Relies on heuristics (e.g., split horizon) | Inherent (checks own ID in path) |
| Scalability | Limited (intra-domain, smaller networks) | High (inter-domain, Internet-scale) |
| Policy Support | Minimal | Extensive (path attributes for decisions) |
| Convergence | Slower, prone to count-to-infinity | Slower but stable, policy-driven |
| Typical Use | Interior routing (e.g., within an organization) | Exterior routing (between ASes) |
Path-vector is considered “advanced” because it addresses key limitations of traditional distance-vector protocols—particularly routing loops and lack of policy control—by including explicit path information, making it suitable for the global Internet.
References:
- Path-vector routing protocol - Wikipedia
- What is the difference between distance vector protocol and path vector protocol - Network Engineering Stack Exchange
- Path Vector vs Distance Vector - Lab1918
- Routing Protocols Compared - Packetcoders
- Distance Vector, Link State, and Path Vector - InformIT