OSPF DR BDR election process
When implementing the OSPF routing protocol, the DR/BDR election process adheres to the following steps:
- Once an OSPF becomes active on a multi-access network, it sets the DR and BDR values to 0.0.0.0 which indicates these are unknown. It also starts a wait timer of the value of the dead interval.
- The router starts neighbor discovery. It sends the 0.0.0.0 values for DR/BDR
- If a received Hello includes values for DR/BDR, these are accepted and the wait timer is stopped
- If the wait timer expires, the DR election starts
- A list of neighbors on the multi-access network is established that are eligible for being DR/BDR (their priority is higher than zero)
- A subset of routers from this list is created. This subset excludes routers listing their own address as the DR (so routers claiming to be the DR are excluded)
- From this subset, select the router with the highest priority/RID/Loopback/Address to be the BDR according to the OSPF DR BDR election criteria
- From the original (not subset list), select the Router with the highest priority/RID/loopback/address to be the DR
- If there are no routers originally claiming to be the DR, then promote the chosen BDR to a DR, and elect another BDR via the same method
Links:
https://forum.networklessons.com/t/ospf-dr-bdr-election-explained/880/62?u=lagapides
Links to this page:
- BGP Route Reflector
- IS-IS - DIS and Pseudonode
- OSPF - Adjacencies in a Multi-Access network segment
- OSPF - BDR is elected before DR
- OSPF - DR-BDR election per broadcast domain
- OSPF - DR-BDR election priority of zero
- OSPF - Link ID and ADV Router in the OSPF database
- OSPF - Link ID in the OSPF database
- OSPF - Neighbor states
- OSPF - Neighbor vs Adjacency
- OSPF - what triggers a DR-BDR election
- OSPF DR BDR election and neighbor adjacencies
- OSPF DR BDR election criteria
- OSPF master slave election
- OSPF network types
- OSPF point to point network type for Ethernet
- OSPF