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OSPF - 'Highest IP'

Discussion in 'Routing & Switching' started by StueyT, May 20, 2007.

  1. StueyT

    StueyT Bit Poster

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    Hello all,

    Just confused over the DR and BDR elections. I understand that it goes in the order of highest priority (50 is higher than 1), and if all are the same, then it goes by highest router ID. Looking at a few labs, this is confusing me. Is 10.0.0.1 higher or lower than 192.168.0.1?

    Cheers
     
    Certifications: CCNA
    WIP: MCDST, MCSA, CCNP, CCSP
  2. r.h.lee

    r.h.lee Gigabyte Poster

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    StueyT,

    The OSPF router with Router ID of 10.0.0.1 is lower than the OSPF router with Router ID of 192.168.0.1 .

    For supporting information, check out the diagram under the "DR Election" section of the "OSPF Design Guide."

    Source:
    1. OSPF Design Guide - Cisco Systems - http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml
    2. DR Election section of the OSPF Design Guide - Cisco Systems - http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml#t21
     
    Certifications: MCSE, MCP+I, MCP, CCNA, A+
    WIP: CCDA
  3. happyone3

    happyone3 New Member

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    well..this topic is something you should lab, because it can be very confusing. Textbooks says that the DR/BDR election in multiaccess will be the router with the highest ip on loopback, meaning that 192.168.0.0 is higher than 10.0.0.0. If no loopback the highest ip address on any interface. If you have some routers multaccess ethernet, you would notice the router you configure first will be the DR, regardless of others routers have have the highest router-id, because there is no preempt.
     
  4. BosonMichael
    Highly Decorated Member Award

    BosonMichael Yottabyte Poster

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    ...until that router is restarted, the BDR becomes the DR, and BDR elections occur.
     
    Certifications: CISSP, MCSE+I, MCSE: Security, MCSE: Messaging, MCDST, MCDBA, MCTS, OCP, CCNP, CCDP, CCNA Security, CCNA Voice, CNE, SCSA, Security+, Linux+, Server+, Network+, A+
    WIP: Just about everything!

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