Re: DR Election: Incase of a Priority Tie, Highest RID Wins -

From: Bob Sinclair (bobsinclair@frontiernet.net)
Date: Thu Jun 01 2006 - 16:25:10 ART

Godswill,

My results differ using two routers running (C3640-JK9O3S-M), Version 12.4(5).
R2 with RID 172.16.102.1 is connected to R6 with RID 172.16.106.1 over
FastEthernet. Otherwise all is default.

Normally, R6 is the DR and R2 is the BDR, based on R6 having the higher RID.

If I shut the R6 interface F0/0, then R2 transistions to DR. When R6 comes
back up it becomes BDR, and stays that way.

At least on this platform, with this IOS, in the month of June, there is a DR
on a 1-router network and boot sequence does determine DR on a 2-router
broadcast segment.

Winning the DR election is like winning a door prize: you must be present to
win. If there is only one router on a broadcast network, it will become the
DR and a router with a higher RID will not preempt.

HTH,

Bob Sinclair
CCIE #10427, CCSI 30427
www.netmasterclass.net

  ----- Original Message -----
  From: Godswill Oletu
  To: Jian Gu
  Cc: Cisco certification
  Sent: Thursday, June 01, 2006 2:34 PM
  Subject: Re: DR Election: Incase of a Priority Tie, Highest RID Wins - Truth
or Fallacy?

  Jian,

  The concept of preemption does not apply in a two router OSPF segment. When
  one router goes down, so does the OSPF ajacency and neigbor relationship
with
  the other router. The second router cannot transistion from a BDR to a DR
all
  by itself, neither will it remain a BDR in the absent of the other router.
So,
  when the old router comes back online, there will be no DR or BDR on that
  segment, the OSPF ajacancy will be renegotiated from the beginning as if it
  never occurred before and so will be the election of DR/BDR.

  HTH
  Godswill Oletu
    ----- Original Message -----
    From: Jian Gu
    To: Godswill Oletu
    Cc: Cisco certification
    Sent: Thursday, June 01, 2006 1:25 PM
    Subject: Re: DR Election: Incase of a Priority Tie, Highest RID Wins -
Truth
  or Fallacy?

    DR does not preempt.

    On 6/1/06, Godswill Oletu <oletu@inbox.lv> wrote:
      Hi,

      This topic was beaten to death the past few weeks on the group and the
  general
      concession is that, when there is a tie on the priority vlaues, the
  highest
      Router-ID wins, Cisco online documentation have various pages
confirming
  this
      as well. But, I do not know if anyone labbed this up and fool-proof
this
      concept.

      I am have labbed that exact scenario, that required that a particular
  router
      be elected the DR in segment of two routers, the neighbor or priority
  commands
      are not to be used.

      The results I am getting is not consistent across the board:

      Little preview of my configures:

      Rack1R2:
      interface Serial0
      no ip address
      encapsulation frame-relay
      no frame-relay inverse-arp
      !
      interface Serial0.204 point-to-point
      ip address 144.1.24.2 255.255.255.0
      ip ospf network broadcast
      frame-relay interface-dlci 204
      !
      router ospf 1
      router-id 222.2.2.2
      log-adjacency-changes
      network 144.1.24.2 0.0.0.0 area 0.0.0.0
      network 150.1.2.2 0.0.0.0 area 0.0.0.0
      !
      ----------------------------------------------------------------------- 

--
  ----
      --
      Rack1R4:
      interface Serial0/0
      no ip address
      encapsulation frame-relay
      no frame-relay inverse-arp
      !
      interface Serial0/0.402 point-to-point
      ip address 144.1.24.4 255.255.255.0
      ip ospf network broadcast
      frame-relay interface-dlci 402
      !
      router ospf 1
      router-id 150.1.4.4
      log-adjacency-changes
      network 144.1.24.4 0.0.0.0 area 0.0.0.0
      network 150.1.4.4 0.0.0.0 area 0.0.0.0
      !
      -----------------------------------------------------------------------
--
  ----
      -------
      Results:
      Rack1R2#clear ip ospf process
      Rack1R2#sho ip ospf nei
      Neighbor ID     Pri   State           Dead Time   Address
  Interface
      150.1.4.4         1   FULL/DR         00:00:37    144.1.24.4
  Serial0.204
      Rack1R2#

      Rack1R4#show ip ospf nei
      Neighbor ID     Pri   State           Dead Time   Address
  Interface
      222.2.2.2         1   FULL/BDR        00:00:32    144.1.24.2
      Serial0/0.402
      Rack1R4#

      Despite the fact that Rack1R4 have the lowest Router-ID, it was elected
  the DR
      for that segment and Rack1R2 who have the highest Router-ID settled for
  the
      less fancy job of a BDR.

      Now............

      Rack1R4#clear ip osp nei
      Rack1R4#sho ip ospf nei
      Neighbor ID     Pri   State           Dead Time   Address
  Interface
      222.2.2.2         1   FULL/DR         00:00:39    144.1.24.2
      Serial0/0.402
      Rack1R4#

      Rack1R2#sh ip ospf nei
      Neighbor ID     Pri   State           Dead Time   Address
  Interface
      150.1.4.4         1   FULL/BDR        00:00:34    144.1.24.4
  Serial0.204
      Rack1R2#

      Now, the roles have been revised, completely negativing the 'supposed'
      influence that a higher Router-ID should have in the DR/BDR election
  process.

      Or, are mine missing something here? Maybe my coffee have not sink in
      yet...but your contribution is highly welcome.

      Thanks.
      Godswill Oletu

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