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7110 Views 3 Replies Latest reply: Mar 19, 2014 11:27 AM by Gary RSS

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DR/ BDR election in ospf

Feb 7, 2012 7:30 AM

samsecure09 37 posts since
Feb 24, 2010

Hello Friends ,

 

I am stuck on one issue.

 

DR is elected first or BDR .Somehow i came to know BDR is elected first ...please explain/documentation for detailed working for this process

 

HOW BDR is elected first ??

 

 

 

 

 

thanks 

  • Elvin Arias 1,830 posts since
    Mar 12, 2010
    Currently Being Moderated
    1. Feb 7, 2012 12:11 PM (in response to samsecure09)
    Re: DR/ BDR election in ospf

    Yeah! I remember the coolest explanation about that from two giants Scott and Petr. I don't going to explain that, because they already did. See the post. https://learningnetwork.cisco.com/thread/33560?start=0&tstart=0

     

    Anyways if you don't understand something, please post.

     

    Elvin

  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    2. Feb 7, 2012 1:13 PM (in response to samsecure09)
    Re: DR/ BDR election in ospf

    Read RFC 2328 section 9.4 Electing the Designated Router.  This explains the process of electing the BDR and DR.  The BDR is elected first.

     

    Hope this helps.

     

    Brian

  • Gary 4 posts since
    Jul 6, 2012
    Currently Being Moderated
    3. Mar 19, 2014 11:27 AM (in response to samsecure09)
    Re: DR/ BDR election in ospf

    How OSPF Forms Its Neighbors  In this topology, all routers are running Open Shortest Path First (OSPF) over the Ethernet network:    This is sample output of the show ip ospf neighbor command on R7 and R8:

     

    R7# show ip ospf neighbor   

    Neighbor ID     Pri       State                       Dead Time   Address         Interface  

    170.170.3.4       1       2WAY/DROTHER    00:00:34    170.170.3.4     Ethernet0   

    170.170.3.3       1       2WAY/DROTHER    00:00:34    170.170.3.3     Ethernet0   

    170.170.3.8       1       FULL/DR         00:00:32    170.170.3.8     Ethernet0   

    170.170.3.2       1       FULL/BDR        00:00:39    170.170.3.2     Ethernet0   

     

    R8# show ip ospf neighbor   

    Neighbor ID     Pri       State                      Dead Time   Address         Interface   

    170.170.3.4       1       FULL/DROTHER    00:00:37   170.170.3.4     Ethernet0   

    170.170.3.3       1       FULL/DROTHER    00:00:37    170.170.3.3     Ethernet0   

    170.170.3.7       1       FULL/DROTHER    00:00:38    170.170.3.7     Ethernet0   

    170.170.3.2       1       FULL/BDR        00:00:32    170.170.3.2     Ethernet0

     

     

    13683-11a.jpg

     

    http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13683-11.html

    Can anyone describe to me why R2 is the BDR?

     

    Regards...

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