OSPFv2 (Open Shortest Path First version 2 is a link-state routing protocol designed for IPv4 networks. It is defined in RFC 2328 and is widely used in enterprise and service provider networks due to its efficiency and scalability.
Key Features
of OSPFv2:
- Maintains a complete topological map of the network (LSDB - Link-State Database).
- Uses the Dijkstra (SPF) algorithm to compute the shortest path to all destinations.
- Divides networks into areas to reduce routing overhead.
- Backbone Area (Area 0) is mandatory; all other areas must connect to it.
Types of
areas:
- Normal Areas (Standard areas)
- Stub Areas (Block external routes)
- Totally Stubby Areas (Block external and inter-area routes)
- Not-So-Stubby Areas (NSSA) (Allows limited external routes)
Metric
(Cost):
- Calculated based on interface bandwidth (Cost = Reference BW / Interface BW, default Reference BW = 100 Mbps).
Packet Types:
- Hello (Discover/maintain neighbors)
- DBD (Database Description) (Exchange LSDB info)
- LSR (Link-State Request) (Request specific LSA)
- LSU (Link-State Update) (Send LSA updates)
- LSAck (Link-State Acknowledgment) (Acknowledge LSUs)
LSA Types
(Link-State Advertisements):
- Type 1 (Router LSA) – Intra-area router info.
- Type 2 (Network LSA) – Multi-access network info.
- Type 3 (Summary LSA) – Inter-area routes (ABR-generated).
- Type 4 (ASBR Summary LSA) – Location of ASBR.
- Type 5 (External LSA) – Routes from other AS (redistributed).
- Type 7 (NSSA External LSA) – External routes in NSSA.
Neighbor
States:
- Down → Init → 2-Way → ExStart → Exchange → Loading → Full
Authentication:
Supports plain-text,
MD5, and SHA authentication for security.
Let's see the configuration of the OSPFv2 subcommand.
Topology:-
- Configure the topology as per the diagram
- Configure the IP addresses as per the topology
- Configure OSPFv2 with the subcommand
- advertise directly connected routes and loopbacks
- Make sure all the routes are exchanged
- Verify with ping and show commands
