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Webcast-Catalyst9k

2-DRs in OSPF

hi all

is it possible to have 2 DRs in a single Broadcast network??

sh ip ospf neighbor o/p :

x.x.x.225 0 FULL/ - 00:00:39 x.x.x.141 Serial5/2

x.x.x.192 0 FULL/ - 00:00:39 x.x.x.185 Serial5/1

x.x.x.225 0 FULL/ - 00:00:39 x.x.x.137 Serial4/4

x.x.x.192 0 FULL/ - 00:00:39 x.x.x.181 Serial4/3

x.x.x.249 1 FULL/DR 00:00:36 x.x.x.33 FastEthernet1/0

a.a.a.149 0 FULL/ - 00:00:39 x.x.y.58 Multilink2

a.a.a.150 0 FULL/ - 00:00:39 x.x.y.42 Multilink1

a.a.a.149 0 FULL/ - 00:00:37 x.x.y.38 Serial5/3

a.a.a.150 0 FULL/ - 00:00:38 x.x.y.62 Serial4/7

x.x.x.249 1 FULL/BDR 00:00:39 x.x.z.1 FastEthernet0/0

x.x.x.251 1 FULL/DR 00:00:39 x.x.z.4 FastEthernet0/0

a.a.a.147 1 2WAY/DROTHER 00:00:35 x.x.z.3 FastEthernet0/0

regds

prem

5 REPLIES
Cisco Employee

Re: 2-DRs in OSPF

The short answer is no. At most one DR and one BDR can exist per subnet. In the output you provided, there is one DR on Fa0/0 and one on Fa1/0.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Re: 2-DRs in OSPF

hi hritter

thx for the reply.i got it

regds

prem

Gold

Re: 2-DRs in OSPF

I concur with Herald, but wanted to ask if you might be referring to the "BDR" listed above? That would be the backup designated router, the router that will take over DR duties if the DR fails or becomes unattached from the network. So, as Herald said, you don't have two DR's on a single network here.

:-)

Russ.W

Re: 2-DRs in OSPF

hi russ

Wht i undestood is .249 consists is configured with 2 different segments and it acts as a ASBR too in my network.

if u notice in the display it acts as DR when it comes to x.x.x.249 for x.x.x.33 segment.

The same is agin deisgnated as BDR for x.x.z.0/27 segment since .251 acts as the DR for x.x.z.0/27 segment.

x.x.x.249 1 FULL/DR 00:00:36 x.x.x.33 FastEthernet1/0

x.x.x.249 1 FULL/BDR 00:00:39 x.x.z.1 FastEthernet0/0

x.x.x.251 1 FULL/DR 00:00:39 x.x.z.4 FastEthernet0/0

i got confused when my sh ip ospf neighbor has shown me 2 DRs .

regds

prem

New Member

Re: 2-DRs in OSPF

There shouldn't be 2 DRs exist on one broadcast network. If it does ...then it's not a broadcast.

So can you display 2 DRs at the BDR?

Is there are 2 DRs if you clear ospf ?

Please check your topology to confirm that the so called 2 DRs exist on the same segment and can community directly!

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