OSPF Multicast Address

dppagc · January 2016

224.0.0.5 is the All OSPF Routers Address (in that case does it mean the DR and DROTHER routers)?

224.0.0.6 - DR address is used to send routing info to DR routers on a network segment

In that case, does the "job scope" of 224.0.0.5 and 224.0.0.6 overlap since they both talk to the DR routers.

Can someone give a flowchart of events for clarity purpose?

atorven · January 2016

224.0.0.5 - Yes, all OSPF routers use this multicast address, doesn't matter which role they are playing
224.0.0.6 - Both the DR and BDR use this multicast address although only the DR processes LSAs

No, the "job scope" is different because on broadcast networks routers will only form full adjacencies with the DR/BDR, this means that the routers will only forward their database information to the all DR/BDR multicast address, the DR will share this information with the other routers on the all ospf routers multicast address, this exchange process is every efficient as you can have lots of routers in the same network.

The above only applies for broadcast networks.

HTH

dppagc · January 2016

But DRothers dont need to talk to DROther routers, so what is 224.0.0.5 for?

For 224.0.0.6 I understand because DR/BDR need to talk to DROthers.

Iristheangel · January 2016

Which material did you use to study for the CCNP R&S? If I recall correctly, you passed recently, right? A lot of this is covered there so it could be good review for you.

All routers who are NOT a DR/BDR (DROther) send their updates to 224.0.0.6 (DR/BDR). In turn, after the DR/BDR are done processing these updates, the DR sends the updates to the rest of the DROther routers on that same segment via 224.0.0.5. This is to optimize the OSPF behavior on a multiaccess segment so flooding only happens through the DR and cuts back on the unnecessary redundant LSAs. Most of the time you see the optimization from flooding come when routers initially boot up

OSPF Multicast Address

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