From: ccie2be (ccie2be@nyc.rr.com)
Date: Thu Jul 21 2005 - 08:48:09 GMT-3
Shanky,
I don't know if this answers your question directly but I can tell you this.
Ospf doesn't use preemption in the election of the DR and BDR. Because of
this ospf is more stable on a broadcast segment. Once a DR is elected, that
router will remain as the DR even if another router on the same segment
comes on line with a higher priority.
This being the case, I guess that its necessary for a non-Dr and non-BDR
router to remember who the DR and BDR were if it were to go down so that
when it comes back up it knows with which routers to re-establish
adjacencies with.
As far as the lab goes, I don't think this detail is that important. What's
really important is that you're aware of this non-preempt behavior so that
when you configure ospf on a broadcast or nbma segment, you know to set the
priority to 0 on routers which should not become the DR or BDR before
bringing the router up on the segment.
HTH, Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Shanky
Sent: Thursday, July 21, 2005 1:20 AM
To: Group Study
Subject: OSPF: Remember old DR 2.1.1.10 (id) ... why ?
Hi,
I got the foll output with debug ip ospf adj when I shut the serial to FR
switch down on the spoke in NBMA mode. Why does the router remember who the
old DR was as shown in the output ? I mean, once new DR is selected, even if
the old DR comes back online (Say after a crash), it doesnt affect.
**Mar 1 16:15:15.799: OSPF: Remember old DR 2.1.1.10 <http://2.1.1.10> (id)
... why does the router remember the old DR?*
*Mar 1 16:15:15.795: OSPF: Interface Serial0/0 going Down
*Mar 1 16:15:15.795: OSPF: 1.1.1.1 <http://1.1.1.1> address
1.1.1.1<http://1.1.1.1>on Serial0/0 is dead, state
DOWN
*Mar 1 16:15:15.795: OSPF: Neighbor change Event on interface Serial0/0
*Mar 1 16:15:15.795: OSPF: DR/BDR election on Serial0/0
*Mar 1 16:15:15.795: OSPF: Elect BDR 0.0.0.0 <http://0.0.0.0>
*Mar 1 16:15:15.795: OSPF: Elect DR 2.1.1.10 <http://2.1.1.10>
*Mar 1 16:15:15.795: OSPF: Elect BDR 0.0.0.0 <http://0.0.0.0>
*Mar 1 16:15:15.795: OSPF: Elect DR 2.1.1.10 <http://2.1.1.10>
*Mar 1 16:15:15.799: DR: 2.1.1.10 <http://2.1.1.10> (Id) BDR: none
*Mar 1 16:15:15.799: OSPF: 2.1.1.10 <http://2.1.1.10> address
1.1.1.2<http://1.1.1.2>on Serial0/0 is dead, state
DOWN
*Mar 1 16:15:15.799: %OSPF-5-ADJCHG: Process 1, Nbr
2.1.1.10<http://2.1.1.10>on Serial0/0 from
FULL to DOWN, Neighbor Down: Interface down or detached
*Mar 1 16:15:15.799: OSPF: Neighbor change Event on interface Serial0/0
*Mar 1 16:15:15.799: OSPF: DR/BDR election on Serial0/0
*Mar 1 16:15:15.799: OSPF: Elect BDR 0.0.0.0 <http://0.0.0.0>
*Mar 1 16:15:15.799: OSPF: Elect DR 0.0.0.0 <http://0.0.0.0>
*Mar 1 16:15:15.799: DR: none BDR: none
**Mar 1 16:15:15.799: OSPF: Remember old DR 2.1.1.10 <http://2.1.1.10> (id)*
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