FAQ ON DYNAMIC ROUTING# INTERVIEW PREP GUIDE ABOUT DYNAMIC (RIP, EIGRP,OSPF) ROUTING
🔹 What is dynamic routing ?
Dynamic routing automatically learns and updates routing table using routing protocols.
🔹 What is the main purpose of dynamic routing ?
To provide automatic path selection, scalability, and failover.
🔹 Which are the main dynamic routing protocols ?
RIP (Distance Vector), EIGRP (Hrbrid) and OSPF (Link-State).
🔹 What is convergence in routing ?
Time taken for all routers to update and agree on network topology.
🔹 Why is dynamic routing preferred over static routing ?
It reduces manual configuration and adapts to topology changes.
🔹 What causes slow convergence ?
Large networks, inefficient protocols, and frequent topology changes.
🔹 What is routing metric ?
A value used to determine the best path (e.g. hop count, bandwidth).
🔹 Default AD values of dynamic protocols ?
RIP: 120 , EIGRP: 90 (internal), 170 (external) and OSPF: 110
🔹 What is load balancing in routing ?
Using multiple paths to send traffic.
🔹 What is equal-cost load balancing ?
Using multiple paths with the same metric.
🔹 What is unequal-cost load balancing ?
Using paths with different metrics (supported by EIGRP).
🔹 What is route redistribution ?
Sharing routes between different routing protocols.
🔹 What is a routing loop ?
A situation where packets circulate endlessly.
🔹 How are loops prevented ?
Using techniques like
1. Split horizon (Prevents sending route updates back through the same interface).
2. Route poisoning (Marking a route as unreachable).
3. Hold-down timers (Prevents routers from accepting incorrect updates for a period of time).
🔹 What is RIP ?
A distance-vector protocol using hop count as metric.
🔹 What is the purpose of RIP ?
Simple routing in small networks (15 hop count only).
🔹 What is difference between RIP version 1 & 2 limitation ?
Classful (no subnet mask support) for Version 1 & Classless (Support VLSM AND CIDR).
🔹 What is RIP convergence speed ?
Slow
🔹 What is EIGRP ?
A hybrid routing protocol (distance-vector + link-state features).
🔹 What is the purpose of EIGRP ?
Fast convergence and efficient routing.
🔹 What metric does EIGRP use ?
Bandwidth & Delay (Default), Reliability and Load.
🔹 What is the EIGRP metric formula ?
Metric = [(10⁷ / min bandwidth) + delay] × 256
🔹 What is feasible successor ?
Backup route in EIGRP.
🔹 What is feasibility condition ?
Reporting distance 'less than' Feasible distance.
= RD : Best metric to reach a destination.
= FD : Distance reported by a neighbor.
🔹 What is reported distance ?
Distance reported by a neighbor.
🔹 What is variance in EIGRP ?
Allows unequal-cost load balancing.
🔹 When should EIGRP be used ?
Medium to large enterprise networks or Enterprise networks needing fast convergence (Cisco based).
🔹 what is OSPF ?
OSPF is a link-state dynamic routing protocol that calculates the shortest path to a destination using the SPF (Dijkstra) algorithm.
🔹 What is the purpose of OSPF ?
Scalable and hierarchical routing.
🔹 What is OSPF metric ?
Cost = Reference Bandwidth / Interface Bandwidth.
100 Mbps (Default reference bandwidth)
🔹 What is an OSPF area and Backbone area ?
Logical group of router and Area 0.
🔹 What is LSA (Link-State Advertisement) ?
Information about network topology.
🔹 What is LSR (Link State Request) ?
Requests specific link-state records from an OSPF neighbor.
🔹 What is LSU (Link State Update) ?
Sends specific link-state records that were requested. This packet is like an envelope with multiple LSAs in it.
🔹 What is LSAck (Link State Acknowledgement) ?
OSPF uses Link State Acknowledgement packets to confirm the receipt of Link-State Advertisements (LSAs), ensuring reliable delivery of routing information.
🔹 What is OSPF neighbor adjacency ?
Relationship formed between routers to exchange routes.
🔹 What are OSPF states ?
Down → Init → 2-Way → ExStart → Exchange → Full.
🔹 What is DR and BDR ?
Designated Router (Central router for LSA exchange in broadcast networks) and Backup Designated Router (Backup of DR).
🔹 When should OSPF be used ?
Large, scalable, and multi-vendor (vendor-neutral) networks.
🔹 How does routing affect bandwidth ?
Efficient routing reduces congestion.
🔹 What is stub network ?
Network with single exit point.
🔹 What is best practice for dynamic routing ?
Use OSPF for large networks, EIGRP for performance, RIP only for learning/small setups.
🔹 What is wildcard mask ?
Inverse of subnet mask.
e.g. Wildcard = 255.255.255.255 – Subnet Mask
🔹 What is summarization in OSPF ?
Combining routes at ABR/ASBR.
🔹 Quick Comparison : -
| Feature | RIP | EIGRP | OSPF |
|---|---|---|---|
| Type | Distance Vector | Hybrid | Link-State |
| Metric | Hop Count | Bandwidth + Delay | Cost |
| Formula | Hops | (10⁷/BW + Delay)×256 | Ref BW / BW |
| Max Size | Small | Medium-Large | Large |
| Convergence | Slow | Fast | Fast |
| Max. Hop | 15 | Unlimited | Unlimited |
| Vendor | Open | Cisco | Open |
🔹 All in One Network Topology : -
