How do two adjacent routers know that they have a two-way OSPF communication ?
Think of the answer before revealing the hidden one !
You may say "they see each other's Hello packets" - but I challenge you: if I'm a router and I see your OSPF Hello, how do I know that you also see my OSPF Hello's ?
The fact that a router sees a Hello packet it only shows an INIT state but it does not ensure a two-way communication. Routers include the list of neighbors in their Hello packets, so a 2-way state is reached when a router sees its own ID in the Hellos received from that particular peer.
The Hello packets also contains the information about DR and BDR - or use 0.0.0.0 if they have not been selected yet.
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Costi is a network and security engineer with over 10 years of experience in multi-vendor environments. He holds a CCIE Routing and Switching certification and is currently pursuing same expert-level certifications in other areas. He believes that the best way to learn and understand networking topics is to challenge yourself to fix different problems, production-wise or lab-type exams. He also enjoys teaching networking and security technologies, whevever there is an opportunity for it.
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