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New Member

Highest ip address of loopback interface does not advertise by ospf proces

my router run ospf with IOS version 120(5), only one loopback interface for each router.

it's said "the router ID will be adverstise to ip router table automatically" , so i haven't include loopback interface in NETWORK statement.

in end, I saw all the OSPF route but the loopback interface .

BRs

5 REPLIES
New Member

Re: Highest ip address of loopback interface does not advertise

Hi,

I hope i understood your question.OSPF doesnt advertize loopback routes so all you will see is your own directly connected loopbackinterface.

If you hadnt defined loopback interface and enables ospf then it will select the highest order ip address as Router ID even if you define the loopback interface after that.You will have to clear ip ospf process and then it will select loopback interface as your Router ID.

Regards,

Bilal

New Member

Re: Highest ip address of loopback interface does not advertise

hello Bilal,

yes i see directly connected loopbackinterface in route table,

but in " Routing TCP/IP volume I " , it is said , "you needn't include Network statement of loopback interface, the loop back interface will be advertised automatically (if the loopback is router ID) , so i think the router's loopback interface , which taken as router ID , will appear in the other's router table.

or how to understand the sentence above.

BRs

Re: Highest ip address of loopback interface does not advertise

Here is the way it works. When you enable OSPF, the OSPF Router ID will be the highest IP address assigned to a physical interface, or the highest IP on a loopback if a loopback is defined. you can also manually specify the OSPF router-id if you want. The Router ID is just a unique 32bit number and doesn't have to be a real IP address assigned to the router. It can be anything. Another vendors default router ID is a hash of the serial # and MAC address for example. After OSPF is enabled/running, the RID will not change itself unless the router is rebooted, OSPF process is cleared, or you remove OSPF and add it back.

The loopback interface will not be advertised via OSPF unless you include a network statement for it under OSPF, or redistribute it into OSPF. If you do include it under router OSPF with a network starement then by default it will be advertised as a host route (32 bit). You can change this behavior by doing a ip ospf network point-to-point on the loopback interface which will cause it to be advertised with the real subnet mask assigned.

Erick

New Member

Re: Highest ip address of loopback interface does not advertise

thanks for your help.

BRs

Biao

New Member

Re: Highest ip address of loopback interface does not advertise

Hi,

If the ospf process have started, the router-id advertised by ospf will not changed until you clear ospf process use "clear ip ospf process" in privilege mode even you config a loopback interface. But if you want to use that address for router-id , you can use "router-id x.x.x.x" inside the "router ospf" mode.

Best Regards

Teru Lei

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