Ospf DR election

[adnane dakna]

Hi .

I need to understand why election of dr is by  multiaccess domain and which type of data are exchange between DR and orher routers

[Nandan Mathure]

Please read from the following link:

http://networkninja.co.za/cisco-systems/open-shortest-path-first-ospf-fundamentals-dr-and-bdr/

Consider this as alternate simplified example: A class of students talking to each other of a message and the same message given to the whole class by a Teacher.

[Kishore Chennupati]

I like ur simplified example Nandhan

[smehrnia]

Hi Adnane,

because in a multiaccess domain (network) every device can talk to other devices, like as its in an ethernet segment.

Therefore, there could be loads of routing data packets going back and forth and multiple adjacencies must be formed between the OSPF peers so they can keep eachother posted about the network's topology and whats happening in the network, so that OSPF works properly.

to overcome this everyone to everyone (full mesh) routing data exchange and peering which of course has a great administrative load and impact on the networks resources and convergence times, they introduced DR / BDR as the center (redundancy with BDR) of the OSPF group. Now, everyone peers with the DR, talks to the DR and then DR relays routing information to all others at once. a one to one - one to many propagation.

information that is exchanged between DR and other routers are Hello messages (periodicaly) and routing information n updates through LSA (Link State Advertisement) messages.

pls Rate if it helped.

Soroush.

[Joseph W. Doherty]

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Posting

As the other posters have noted, DR/BDR avoids the need for every OSPF router on the same shared segment the need to directly "talk" to each other.  Another advantage, OSPF can share information on the common segment using multicast.

[adnane dakna]

Hello ,

Thanks for all your contributions , Now the concept of DR is obvious for me .

regards

[smehrnia]

No problem Adnane,

please rate the answers and mark your question as Answered so others with the same interests can easily find the suitable discussion. lets be helpful

Soroush.