OSPF - IBGP peering with non backbone router.

sunny81

I am preparing in JNCIP-M.
I feel bit of confusion in the JNCIP book on OSPF as IGP part.
From the book, only required to include interface lo0 into OSPF configuration at backbone /area 0.
For the sub-area, there is no inclusive of lo0 in OSPF configuration.

It caused when i building the IBGP and and peering with those sub-area IGP's loopback add, cannot established the peering. i have to configure lo0 into OSPF only peering is up.

Any expert here could clarify it?

hoogen82

I am assuming it is introduction of loopback as type 3 in backbone and the rest would be type 1... there is no way they would have told not to include the loopback under OSPF

zoidberg

if i still have any memory left....

back in the day, loopback was automatically advertised into ospf. 8.4? 8.5? that changed and you need to specify it.

zoidberg

from 8.5 release notes

OSPF link-state advertisements—Beginning with JUNOS Release 8.5, OSPF no longer advertises a router identifier interface that is not configured to run OSPF as a stub network in its link-state advertisements. [Routing Protocols]

so, back when the book was written, if you used your loopback as the router-id, it was automatically advertised into ospf. i think if you used the router-id command, and that id was different that the loopback ip, then you had to add the loopback to ospf to have it advertise.

zoidberg

JUNOS Enterprise Routing, Page 89

To paraphrase...
JUNOS would automatically advertise a stub route to the router-id interface, so you didn't need to run an IGP on your loopback. 8.5 onward, you need to enable OSPF on the loopback if you want to advertise it in OSPF.

sunny81

No wonder, i am using 9.4 and 9.5 machines to practice.
What version will be using in exam? 8.5?
Thanks

zoidberg

i don't recall what the M was.... 8.1 maybe? ER was 8.4, i think. could be completely different now, both of these values are subject to change at any time. by the time the new labs launch i would expect the code to be drastically different and hopefully a bit recent

the exams do not really focus on code related features, but i guess you will need to be prepared for changes in behavior like this. when you register for an exam, i believe they tell you what code is being used. if not, you can ask. you could even just ask now. either i asked, or they told me during registration, one way i knew what i was walking into.

thankfully, study material like the ER book mentioned issues like this change in ospf behavior.