OSPF DR/BDR selection By Loopback Configuration GNS3 Lab:

OSPF select a DR and BDR on shared Ethernet configuration. Connect and configure the router according to topology given below.

What is DR BDR:
 OSPF select a DR on Ethernet to avoid the broadcast, when there is a DR then all requests are forward by DR only in this case router doesn’t broadcast.  By default a router with high priority is DR, if all have same priority then router with higher physical IP address is DR. And if loopback interface is configure on router then this router is DR and at last higher loopbacks wins.

R1 config:

R1(config-if)#  interface FastEthernet2/0
R1(config-if)#  ip address
R1(config-if)#  no shut
R1(config)# router ospf 1
R1(config-router)#network 10.0.0 area 0

R2 config:

R2(config)# interface FastEthernet2/0
 R2(config-if)# ip address
 R2(config)# ip ospf 1 area 0
R2(config-if)#  no shut
R2(config)# router ospf 1
R2(config-router)# Router-id

R3 config:

R3(config)# interface FastEthernet1/0
 R3(config-if)# ip address
 R3(config-if)# ip ospf 1 area 0
R3(config-if)#  no shut
R3(config)# router ospf 1
R3(config-router)# Router-id

When you complete the above configuration R3 is Select as DR, because  have higher RID and IP address.

But we want to make the R1 as DR, therefore I configure a loopback interface on R1. And then restart the OSPF process by using command “Clear ip ospf process” on all routers
R1(config)#  interface loopback 1
R1(config-if)#  ip address
R1#Clear ip ospf process
R2#Clear ip ospf process
R3#Clear ip ospf process

Now check again the R1 status by “sh ip ospf neigh” command. R2 is BDR and R3 is DR-other.


No comments:

Post a Comment