Comprehensive and Detailed in-depth Step-by-Step Explanation:
OSPF routers establish neighbor relationships and progress through various states during the adjacency formation process. TheExStart stateis where routers negotiate the master and slaveroles. This negotiation is critical because the master initiates the Data Description (DD) packet exchange process.
Here's a breakdown of the relevant OSPF states:
ExStart State:
This is the phase where the routers determine which one will act as the master and which will be the slave.
The decision is based on theRouter IDsof the two routers. The router with the higher Router ID becomes the master.
Exchange State:
After the master-slave roles are established, the routers exchange DD packets. These packets contain summaries of the LSAs in their respective LSDBs.
2-way State:
This state indicates that bidirectional communication has been established between the two routers, but it occurs before master-slave negotiation.
Init State:
This is an early state where a router has sent a Hello packet to its neighbor but has not yet received a Hello packet in response.
Key Point:
The negotiation of master and slave roles happens exclusively in theExStart state, makingD. ExStartthe correct answer.
References:
Huawei HCIA-Datacom Study Guide, Chapter on "OSPF Neighbor States".
RFC 2328 - OSPF Version 2 (Section 10.8).