OSPF

What this topic solves

Link-state routing, adjacencies, LSDB, SPF, areas, LSAs, summarization, redistribution and troubleshooting.

Follow state and packet path

Start with next-hop reachability, RIB/FIB and route source. Then validate protocol state, policy, metrics, attributes and convergence.

Input → classification/state → decision → table → next-hop/output → counters

Design before configuration

• Define the failure domain and expected convergence behavior.
• Document addressing, identifiers, timers, MTU and policy boundaries.
• Prefer explicit, observable state over assumptions.
• Plan rollback and out-of-band access before risky changes.

Commands and verification

Command syntax varies by platform and software release. The examples below come from the existing portal content and must be validated against the target platform documentation before production use.

Down → Init → 2-Way → ExStart → Exchange → Loading → Full

# Cisco IOS/IOS XE
show ip ospf
show ip ospf neighbor
show ip ospf interface
show ip ospf database
show ip route ospf

# MikroTik RouterOS v7
/routing/ospf/instance/print detail
/routing/ospf/area/print detail
/routing/ospf/interface-template/print detail
/routing/ospf/neighbor/print detail
/routing/route/print where protocol=ospf

Evidence-driven workflow

1. Define source, destination, time window and exact symptom.
2. Establish the expected healthy state and compare it with the observed state.
3. Inspect counters, tables, logs and packet captures before resets.
4. Test one hypothesis at a time and prefer reversible changes.
5. Repeat the original test after correction and check side effects.

OSPFv2 / OSPFv3 RFCs

Use the current standard/RFC and the documentation for the exact software release being operated. Vendor syntax is an implementation detail; protocol behavior should be understood independently.

Prove the behavior in a controlled topology

Build the smallest topology that reproduces the mechanism, capture control and data traffic, introduce one deliberate failure and diagnose it before applying the fix.

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