3

About OSPF DR/BDR Routers.

enter image description here

If a link like the one on the top left corner goes down, the router will let the DR and BDR know by generating a Link-state Update Message and sending it using the multicast address 224.0.0.6 and then the DR will forward this information to other routers using the multicast address 224.0.0.5. Since DROTHER routers (the bottom routers) only have a two-way neighbor state with eachother, they wouldn't try to forward any LSUs to their two-way neighbors to let them know what happened, thus eliminating unecessary congestion.

However, would they try to generate and forward a LSU to the BDR router? Since they have a full adjacency with it.

Thank you in advance.

Improve this question

1 Answer 1

Reset to default
5

When a DROTHER has a Routing Update:

  • The Drother sends an LSU to 224.0.0.6 - It is received by DR & BDR
  • The DR forwards the LSU to 224.0.0.5 - It is received by everyone on the link
  • The BDR replies with an LSAck to 224.0.0.5 - (received by everyone, including DR)
  • The remaining DRothers on the link also send an LSAck to 224.0.0.6 - (received by DR & BDR)

This is all outlined in this screenshot below, taken from my video on DRs and BDRs...

enter image description here

Your question:

However, would they try to generate and forward a LSU to the BDR router? Since they have a full adjacency with it.

In a way, yes, since the LSU is sent to 224.0.0.6 both the DR and BDR get it. But there isn't an additional LSU sent specifically to the BDR.

Improve this answer
0

Not the answer you're looking for? Browse other questions tagged or ask your own question.