In OSPF, routers exchange link-state information in different stages to establish full adjacency. TheMTU size is checked during theExchangestate.
Step-by-Step Breakdown:
* OSPF Adjacency Process:
* OSPF routers go through multiple stages when forming an adjacency:Down,Init,2-Way,ExStart, Exchange,Loading, andFull.
* Exchange State:
* During theExchangestate, OSPF routers exchangeDatabase Description (DBD)packets to describe their link-state databases. TheMTU sizeis checked at this stage to ensure both routers can successfully exchange these packets without fragmentation.
* If there is anMTU mismatch, the routers may fail to proceed past the Exchange state.
Juniper Reference:
* MTU Checking in OSPF: Junos uses the Exchange state to check for MTU mismatches, ensuring that routers can properly exchange database information without packet fragmentation issues.