OSPF Multi-Area Configuration

Lessons Discussion
43

why all the areas must be connected to area 0 in OSPF?

44

Hello Diksha

Take a look at this NetworkLessons note why a backbone area is necessary for OSPF. If you have any further questions, let us know!

I hope this has been helpful!

Laz

45

Hello.

Why are the loopback advertised with a 32bit mask while having a 24bit mask?

Thanks for the good article.

46

Hello Oussama

Take a look at this NetworkLessons note on the topic of advertising loopback networks on OSPF.

I hope this has been helpful!

Laz

1 Like
47

Hello,
I have made this lab myself in Packet Tracer, and I have the below output in R2 which is different from what’s mentioned in the article:

R2#show ip ospf neighbor 


Neighbor ID     Pri   State           Dead Time   Address         Interface
192.168.12.1      1   FULL/BDR        00:00:35    192.168.12.1    GigabitEthernet0/0
4.4.4.4           1   FULL/BDR        00:00:39    192.168.24.4

Note that it shows to me the neighbor ID is 192.168.12.1, and it seems this is the correct one, while for Rene in the article the neighbor ID is 192.168.13.1

Can someone explain this to me please?

48

Hello Siraj

The output shown in the lesson is incorrect. It should indeed show a neighbor ID of 192.168.12.1 as in your output. I will let Rene know to make the correction on the lesson.

Thanks for pointing that out!

Laz

1 Like
49

Hello, The output below is from “OSPF Multi-Area Configuration” lecture can someone explain why there are two “BDR’s”? There should only be one I thought. Thanks.

R2#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
192.168.13.1      1   FULL/**BDR**        00:00:34    192.168.13.1    GigabitEthernet0/1
4.4.4.4           1   FULL/**BDR**        00:00:30    192.168.24.4    GigabitEthernet0/2
50

Hello Marcus

Remember that the purpose of a DR/BDR election is to select one OSPF router per broadcast domain to be the central point with which all other OSPF routers will become neighbors. This is the case for all multi-access technologies, where you can have multiple OSPF routers sharing the same network segment.

Now R2 in the lesson is connected to two broadcast domains, the one connected to its Gi0/1 interface, and the one connected to its Gi0/2 interface. Thus, it takes part in two elections. According to the output of the show ip ospf neighbor command, in both cases, it has been elected as the BDR.

If a router has 10 Ethernet interfaces, it will take part in 10 DR/BDR elections because it is connected to 10 network segments. So it may become DR for some, BDR for others, and DROTHER for still others.

I hope this has been helpful!

Laz

51

Yes, This is very helpful. Thank You!

1 Like