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OSPF

OSPF

Open Shortest Path First, the link-state IGP behind most enterprise networks. Articles tagged OSPF cover neighbor relationships, LSA types, areas, DR/BDR election, and Cisco IOS XE configuration.
46 posts
Common OSPF Passive Interface Mistakes
OSPF

Common OSPF Passive Interface Mistakes

Classic OSPF passive-interface mistakes: making uplinks passive by accident, leaving user VLANs active, and using passive-default without exclusions. Here are the fixes.
J
1 min read
Fixing Duplicate OSPF Router ID Issues
OSPF

Fixing Duplicate OSPF Router ID Issues

Two OSPF routers with the same Router ID corrupts the LSDB. Here is how duplicates happen, the log messages to look for, and how to fix them without a full OSPF restart.
J
3 min read
OSPF MTU Mismatch: Symptoms and Fixes
OSPF

OSPF MTU Mismatch: Symptoms and Fixes

OSPF stuck in ExStart or Exchange is almost always an MTU mismatch. Here is what the debug looks like, why it happens during DBD exchange, and how to fix it.
J
4 min read
Fixing OSPF Area Mismatch Issues
OSPF

Fixing OSPF Area Mismatch Issues

Different area IDs on either side of a link means no OSPF adjacency. Here is how to confirm the mismatch with show and debug, and the network statement fix.
J
1 min read
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