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How Designated Router (DR)/Backup Designated
Router (BDR) elected in OSPF http://iwing.wordpress.com
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Topology yang digunakan adalah sebagai berikut :
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On multiaccess network, OSPF elects a DR to be the collection and distribution point for LSA's
sent and received. A BDR is also elected in case the DR fails. All other router becomes DRothers.
How do the DR and BDR get elected?
1. DR: Router with the highest OSPF interface priority
(The Priority is set to 128 by default by JUNOS software)
2. BDR: Router with second highest OSPF interface priority
3. If OSPF interface priorities are equal, the highest router ID is used to break the tie.
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contoh konfigurasi:
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Router cnc1
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[edit interfaces]
root@cnc1# show
fxp0 {
unit 0 {
family inet {
address 192.168.10.1/24;
}
}
}
lo0 {
unit 0 {
family inet {
address 1.1.1.1/32;
}
}
}
[edit interfaces]
root@cnc1#
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[edit protocols]
root@cnc1# show
ospf {
area 0.0.0.0 {
interface lo0.0 {
passive;
}
interface fxp0.0 {
}
}
}
[edit protocols]
root@cnc1#
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[edit routing-options]
root@cnc1# show
router-id 1.1.1.1;
[edit routing-options]
root@cnc1#
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Router cnc2
-----------------------------------------------------------
[edit interfaces]
root@cnc2# show
fxp0 {
unit 0 {
family inet {
address 192.168.10.2/24;
}
}
}
lo0 {
unit 0 {
family inet {
address 2.2.2.2/32;
}
}
}
[edit interfaces]
root@cnc2#
-----------------------------------------------------------
[edit protocols]
root@cnc2# show
ospf {
area 0.0.0.0 {
interface lo0.0 {
passive;
}
interface fxp0.0 {
}
}
}
[edit protocols]
root@cnc2#
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[edit routing-options]
root@cnc2# show
router-id 2.2.2.2;
[edit routing-options]
root@cnc2#
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Router cnc3
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[edit interfaces]
root# show
fxp0 {
unit 0 {
family inet {
address 192.168.10.3/24;
}
}
}
lo0 {
unit 0 {
family inet {
address 3.3.3.3/32;
}
}
}
[edit interfaces]
root#
-----------------------------------------------------------
[edit protocols]
root@cnc3# show
ospf {
area 0.0.0.0 {
interface lo0.0 {
passive;
}
interface fxp0.0;
}
}
[edit protocols]
root@cnc3#
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[edit routing-options]
root@cnc3# show
router-id 3.3.3.3;
[edit routing-options]
root@cnc3#
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Dengan konfigurasi diatas dapat disimpulkan sementara, bahwa yang akan menjadi DR adalah Router
cnc3 karena memiliki router ID yang paling tinggi, dan yang menjadi BDR adalah Router cnc2.
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How to check (OSPF Adjacency and Neighbors)
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[edit]
root@cnc1# run show ospf neighbor
Address Interface State ID Pri Dead
192.168.10.3 fxp0.0 Full 3.3.3.3 128 33
192.168.10.2 fxp0.0 Full 2.2.2.2 128 38
[edit]
root@cnc1#
[edit]
root@cnc1# run show ospf interface
Interface State Area DR ID BDR ID Nbrs
fxp0.0 DRother 0.0.0.0 3.3.3.3 2.2.2.2 2
lo0.0 DRother 0.0.0.0 0.0.0.0 0.0.0.0 0
[edit]
root@cnc1#
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[edit]
root@cnc2# run show ospf neighbor
Address Interface State ID Pri Dead
192.168.10.3 fxp0.0 Full 3.3.3.3 128 37
192.168.10.1 fxp0.0 Full 1.1.1.1 128 34
[edit]
root@cnc2#
[edit]
root@cnc2# run show ospf interface
Interface State Area DR ID BDR ID Nbrs
fxp0.0 BDR 0.0.0.0 3.3.3.3 2.2.2.2 2
lo0.0 DRother 0.0.0.0 0.0.0.0 0.0.0.0 0
[edit]
root@cnc2#
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[edit]
root@cnc3# run show ospf neighbor
Address Interface State ID Pri Dead
192.168.10.2 fxp0.0 Full 2.2.2.2 128 33
192.168.10.1 fxp0.0 Full 1.1.1.1 128 32
[edit]
root@cnc3#
[edit]
root@cnc3# run show ospf interface
Interface State Area DR ID BDR ID Nbrs
fxp0.0 DR 0.0.0.0 3.3.3.3 2.2.2.2 2
lo0.0 DRother 0.0.0.0 0.0.0.0 0.0.0.0 0
[edit]
root@cnc3#
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Only DR sends network LSAs (LSA Type 2) to all other routers on the broadcast segment.
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[edit]
root@cnc1# run show ospf database network extensive
OSPF link state database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Network 192.168.10.3 3.3.3.3 0x8000000c 2068 0x22 0x68a 36
mask 255.255.255.0
attached router 3.3.3.3
attached router 2.2.2.2
attached router 1.1.1.1
Aging timer 00:25:31
Installed 00:34:26 ago, expires in 00:25:32
Last changed 00:34:26 ago, Change count: 8
[edit]
root@cnc1#
-----------------------------------------------------------
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[edit]
root@cnc2# run show ospf database network extensive
OSPF link state database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Network 192.168.10.3 3.3.3.3 0x8000000c 1895 0x22 0x68a 36
mask 255.255.255.0
attached router 3.3.3.3
attached router 2.2.2.2
attached router 1.1.1.1
Aging timer 00:28:25
Installed 00:31:33 ago, expires in 00:28:25
Last changed 00:31:33 ago, Change count: 9
[edit]
root@cnc2#
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[edit]
root@cnc3# run show ospf database network extensive
OSPF link state database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Network *192.168.10.3 3.3.3.3 0x8000000c 2130 0x22 0x68a 36
mask 255.255.255.0
attached router 3.3.3.3
attached router 2.2.2.2
attached router 1.1.1.1
Gen timer 00:14:30
Aging timer 00:24:30
Installed 00:35:30 ago, expires in 00:24:30, sent 00:35:29 ago
Last changed 00:35:30 ago, Change count: 10, Ours
[edit]
root@cnc3
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Sekarang kita akan merubah nilai priority default Router cnc1 dan cnc2, sehingga DR menjadi cnc1
dan BDR adalah cnc2
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root#
[edit protocols ospf]
root@cnc1# set area 0 interface fxp0.0 priority 130
[edit protocols ospf]
root@cnc1#
root@cnc2# set area 0 interface fxp0.0 priority 129
[edit protocols ospf]
root@cnc2#
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How to check (OSPF Adjacency and Neighbors)
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[edit]
root@cnc1# run show ospf interface
Interface State Area DR ID BDR ID Nbrs
fxp0.0 DR 0.0.0.0 1.1.1.1 2.2.2.2 2
lo0.0 DRother 0.0.0.0 0.0.0.0 0.0.0.0 0
[edit]
root@cnc1#
[edit]
root@cnc1# run show ospf neighbor
Address Interface State ID Pri Dead
192.168.10.2 fxp0.0 Full 2.2.2.2 129 30
192.168.10.3 fxp0.0 Full 3.3.3.3 128 35
[edit]
root@cnc1#
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edit]
root@cnc2# run show ospf interface
Interface State Area DR ID BDR ID Nbrs
fxp0.0 BDR 0.0.0.0 1.1.1.1 2.2.2.2 2
lo0.0 DRother 0.0.0.0 0.0.0.0 0.0.0.0 0
[edit]
root@cnc2#
[edit]
root@cnc2# run show ospf neighbor
Address Interface State ID Pri Dead
192.168.10.1 fxp0.0 Full 1.1.1.1 130 35
192.168.10.3 fxp0.0 Full 3.3.3.3 128 33
[edit]
root@cnc2#
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[edit]
root@cnc3# run show ospf interface
Interface State Area DR ID BDR ID Nbrs
fxp0.0 DRother 0.0.0.0 1.1.1.1 2.2.2.2 2
lo0.0 DRother 0.0.0.0 0.0.0.0 0.0.0.0 0
[edit]
root@cnc3#
[edit]
root@cnc3# run show ospf neighbor
Address Interface State ID Pri Dead
192.168.10.1 fxp0.0 Full 1.1.1.1 130 34
192.168.10.2 fxp0.0 Full 2.2.2.2 129 36
[edit]
root@cnc3#
-----------------------------------------------------------
Only DR sends network LSAs (LSA Type 2) to all other routers on the broadcast segment.
-----------------------------------------------------------
[edit]
root@cnc1# run show ospf database network extensive
OSPF link state database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Network *192.168.10.1 1.1.1.1 0x80000010 443 0x22 0x8e08 36
mask 255.255.255.0
attached router 1.1.1.1
attached router 2.2.2.2
attached router 3.3.3.3
Gen timer 00:42:37
Aging timer 00:52:37
Installed 00:07:23 ago, expires in 00:52:37, sent 00:07:23 ago
Last changed 00:07:23 ago, Change count: 16, Ours
[edit]
root@cnc1#
-----------------------------------------------------------
-----------------------------------------------------------
[edit]
root@cnc2# run show ospf database network extensive
OSPF link state database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Network 192.168.10.1 1.1.1.1 0x80000010 412 0x22 0x8e08 36
mask 255.255.255.0
attached router 1.1.1.1
attached router 2.2.2.2
attached router 3.3.3.3
Aging timer 00:53:07
Installed 00:06:51 ago, expires in 00:53:08
Last changed 00:06:51 ago, Change count: 4
[edit]
root@cnc2#
-----------------------------------------------------------
[edit]
root@cnc3# run show ospf database network extensive
OSPF link state database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Network 192.168.10.1 1.1.1.1 0x80000010 467 0x22 0x8e08 36
mask 255.255.255.0
attached router 1.1.1.1
attached router 2.2.2.2
attached router 3.3.3.3
Aging timer 00:52:13
Installed 00:07:46 ago, expires in 00:52:13
Last changed 00:07:46 ago, Change count: 2
[edit]
root@cnc3#
"------------Sekian dulu, semoga bermanfaat----------------"
Ref:
[1]. Junos,OSPF Designated Router.
URL: http://sites.google.com/site/amitsciscozone/home/juniper-junos, (Juli 2010)
