Loopback interface influence in OSPF.

[binoyingen]

Hi ,

can anyone help me to understand what happens in OSPF with the Router has 2 loop back interface configured and one loop back is configured with public IP for DMVPN purpose. My question is whether the Loopback interface with Public IP also advertise in OSPF rooting table if so how to eliminate.

[Mark Malone · Accepted solution]

Hi

It will only advertise in ospf if you have allowed it in the router process ospf  as a network statement in the router itself , you can check if its advertised with show ip route ospf or look through the running config to the section router ospf x , under that section you can see what networks have been advertised specifically

[binoyingen]

Hi Mark,

Thanks for your response !!!! 

my config looks like below : 

interface Loopback1
ip address 192.168.168.168 255.255.255.255

router ospf 100
redistribute static subnets
network 172.16.0.0 0.0.255.255 area 0
network 192.168.10.0 0.0.0.255 area 0

oom-dmvpn-Rtr2# sh ip ospf summary-address

OSPF Router with ID (192.168.168.168) (Process ID 100)

but i could see my loopback IP is showing as RID for ospf process because of high value interface, what happens if i configure another loopback interface with public IP like below, whether it will affect my existing OSPF process.

kindly suggest.

interface Loopback1
ip address 62.x.x.x 255.255.255.255

[Mark Malone · Accepted solution]

Hi

this is being used as the rid  its not specifically advertised per say in the routing process as your only advertising the class C 192.168.10.x network , that's by default its chosen that loopback as rid on startup , if you add in the 62 ip address it wont make a difference to the rid as its lower ip loopback than 192 so it shouldn't effect anything

also you can manually specify the rid so it doesn't change on you

router ospf x

router-id   x.x.x.x

[binoyingen]

Thanks Mark for your valuable inputs !!!!!!