Month: August 2019

Flowchart illustrating the progression of OSPF neighbor states from Down to Full State
CCNA August 31, 2019

OSPF Router States and OSPF Process Explained

When an OSPF router is first connected to a network, it follows a link-state routing process to achieve convergence. This involves building adjacencies, exchanging information, and progressing through various neighbor states. We’ll start with the overall OSPF process before diving into the states. OSPF Process Overview Step 1: Create Adjacencies with Neighbors An OSPF-configured router […]
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Diagram of OSPF Hello packet structure showing header and Hello fields between routers in an enterprise network
CCNA August 31, 2019

Master OSPF Hello Packets: Essential Guide for Cisco Certification (Updated 2025)

OSPF Hello packets (Type 1) are sent periodically on all interfaces, including virtual links, to establish and maintain neighbor adjacencies. Multicast to 224.0.0.5 (AllSPFRouters), these packets enable dynamic discovery of neighboring routers. They advertise parameters for adjacency and elect Designated Routers (DR) and Backup Designated Routers (BDR) on multi-access networks. Point-to-point links skip DR/BDR election. […]
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Diagram of OSPF encapsulation process showing data-link frame, IP packet, and OSPF packet headers between routers in an enterprise network
CCNA August 31, 2019

Master OSPF Encapsulation: Essential Guide for Cisco Certification (Updated 2025)

Open Shortest Path First (OSPF) operates at the Internet Protocol’s network layer, encapsulated solely by IP and local data-link headers. This encapsulation enables efficient routing in enterprise networks. When transmitted over Ethernet, OSPF messages include a data-link frame header, an IP packet header (with protocol field 89), and an OSPF packet header, ensuring reliable delivery. […]
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Illustration of OSPF packet flow between routers, highlighting Hello, DBD, LSR, LSU, and LSAck packets in an enterprise network topology.
CCNA August 31, 2019

Master OSPF Packets Type: Essential Knowledge for Cisco Certification (Updated 2025)

Open Shortest Path First (OSPF) is a powerful link-state routing protocol widely used in enterprise networks and a key topic for CCNA and CCNP certifications. OSPF relies on five distinct packet types to establish neighbor adjacencies, exchange routing information, and maintain a consistent Link-State Database (LSDB) across routers in an area. Understanding these OSPF packets—Hello, […]
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Visual comparison of Single-Area OSPF (Area 0) vs. Multi-Area OSPF (Areas 0, 5, 10) with router icons, ideal for CCNA and CCNP learning
CCNA August 31, 2019

Understanding Single-Area OSPF vs. Multi-Area OSPF

Open Shortest Path First (OSPF) is a link-state routing protocol widely used in enterprise IP networks for its efficiency and scalability. Unlike distance-vector protocols like RIP, OSPF uses a hierarchical design, segmenting networks into areas to optimize routing. Each area consists of routers sharing identical Link-State Databases (LSDBs), containing topology information. For CCNA and CCNP […]
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Diagram of link-state routing operation stages including establishing neighbor adjacencies with Hello packets, exchanging LSAs, building LSDB, creating SPF tree, and populating forwarding database.
CCNA August 31, 2019

Link State Operation – Exclusive Explanation (Updated 2025)

Link state routing protocols, such as OSPF and IS-IS, are fundamental in modern networks due to their efficiency and scalability. For CCNA and CCNP students, mastering link-state operations is crucial for exams and real-world troubleshooting. This article dives into how these protocols work, focusing on OSPF as the primary example. Unlike distance-vector protocols, link-state protocols […]
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OSPF overview diagram with Edsger W. Dijkstra portrait and components including hardware, databases, routing protocol messages, and algorithm connected to central OSPF node.
CCNA August 31, 2019

Introduction to Open Shortest Path First (OSPF)

Open Shortest Path First (OSPF) is a link-state routing protocol replacing the distance vector routing protocol, RIP. RIP was acceptable in the early days of networking. RIP uses hop count as the metric, which does not work better in the larger network. Open Shortest Path First (OSPF) has many advantages over RIP. It can scale […]
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Diagram illustrating route lookup and forwarding in a routing table with networks 172.16.0.0/16, 172.16.1.0/24, 172.16.2.0/24, and packet destination 172.16.2.100 sent to Ethernet1/1.
CCNA August 30, 2019

Best Route, Routing Table Terms, and Lookup Process (Updated 2025)

The best route is the longest match route to the destination IP address. The route lookup process matches the destination IP address with the available routes in the routing table and selects the longest-matched route as the forwarding route. To match the destination IPv4 address of a packet with the routes in the routing table, […]
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Cisco routing table entry diagram with D code for EIGRP route to 182.168.0.0 network via Serial0/1/0.
CCNA August 30, 2019

What is the Routing Table Entries

The routers are typically responsible for directing traffic across multiple networks. Each router maintains a list of known networks and directions in its routing table. The router performs a routing table entries lookup to find the proper interface that leads to the destination address. Each entry in a routing table is called a “route entry: […]
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Illustrated diagram of link-state routing protocol steps showing routers in discovery, hello protocol, LSP building, and flooding phases.
CCNA August 30, 2019

Link-State Routing Protocol

Link-state routing protocols are also known as shortest-path first protocols. They maintain a complete picture of all the routers running a link-state routing protocol in the complete network. All routers running a link-state routing protocol originate information about themselves and their directly connected routers, links, and the state of those links as multicast messages. The […]
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