Blog

OSPF supports plain-text, MD5, and SHA authentication at the interface or area level. Here is how to configure each, why MD5 is the production default, and how to verify.

Multi-area OSPF across Area 0, 10, and 20 with two ABRs. Full R1 to R5 config plus show commands to confirm inter-area routes and ABR behavior.

The default-information originate command injects 0.0.0.0/0 as a Type 5 LSA and turns the router into an ASBR. Here is the syntax, the always option, and verification.

Classic OSPF passive-interface mistakes: making uplinks passive by accident, leaving user VLANs active, and using passive-default without exclusions. Here are the fixes.

OSPF learned the route but it is not in the routing table. Walk through AD conflicts, passive interfaces, distribute-lists, and next-hop reachability step by step.

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.