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What Is OSPF Router LSA? (Link ID, Routing Table OSPF 2.1)

Q1. What is OSPF Router LSA? Answer: It is also called Type-1 LSA. A router running OSPF creates a Type-1 LSA to describe its interface IP addresses and costs. When starting OSPF, the router creates a Type-1 LSA to describe its links. Q2. Why Type-1 LS... Read >

What Is OSPF Network LSA? (Link ID, Attached Routers, 2.1)

Q1. What is DR? Answer: DR stands for Designated Router. In a multiacces subnet (E.g., Ethernet), one routers with higher priority/router ID is elected as DR. DR is responsible to maintain a Full Adjacency relationship with each non-DR routers. That is,... Read >

Traceroute Basics Tutorial - TTL, Time Exceeded (FAQ From a Simulation)

This article is the FAQ of a traceroute simulation tutorial. It covers packet structure, error code, topology, and operation flow. Q1. What is Traceroute? Answer: Traceroute is a network diagnostic tool. It is used to discover next hops along the path to... Read >

Stub Area For Beginners (ABR As Default Gateway For Internal Routers 3.1)

1. What is OSPF Stub Area? Answer: In a stub area, OSPF internal routers don't keep external destinations. They use ABR as default gateway to reach external destinations outside OSPF AS. That is, routers don't have type 4, 5 LSA. 2. What is Totally Stu... Read >

OSPF Simulation Tutorial for Beginners (Interactive, Visual)

OSPF is a complex protocol. To help beginners grasp abstract its concepts, a different approach is taken -- Visualizing OSPF simulation. This tutorial, OSPF basic, simulates the basic OSPF activities on a simple topology: H1-R1-R2-H2. R1 and R2 are router... Read >

How Does OSPF Neighbor State Change? (OSPF Simulation - Interactive, Visual)

Q1. What are OSPF packets? What do they do? Answer: There are 5 OSPF packets: Hello: Discover neighbors. DD (Data Description): Exchange LSDB catalog (LSA headers). Request: Ask neighbor to send LSA that I don't have. Update: Send LSA requested ... Read >

OSPF Simulation - DR Election for Beginners (Visual, Interactive)

Q1. What is neighbor list? Answer: Each OSPF router uses a neighbor list to track its neighbors discovered, their states, who is DR/BDR it has elected. Q2. How is it being used? Answer: When a router floods a Hello, it wants to tell neighbors about its... Read >

IP Addressing Basics Tutorial - Why IP Address Is Required? (Interactive Animation 1)

This is the first tutorial of IP address series. It is followed by How Internet forwards packets, Network address, Classful, and Subnetting. Q1. Why IP address is required? Answer: Telephones are connected to phone network to exchange voice messages. A... Read >

IP Subnetting Tutorial (Classless) - With Interactive Examples and Simulation 5

Q1. What is classless IP address? Answer: Classless is also called IP subnetting. It divides classful network addresses into smaller networks (subnet). The rules are simple: - In classful addressing scheme, a 32 bit address is divided into Network ID and... Read >

IP Addressing Tutorial - How Internet Forwards Packets? (Interactive Animation 2)

Q1. What's the relationship between Internet and routers? Answer: First, let's learn what is Internet? Computers are able to exchange messages by connecting to Internet. When receiving a message transmitted from one computer to another computer, Interne... Read >