OSPF multi-area configuration issue

[Noqqio]

Hi! I'm setting ip an OSPF network using 4 different areas. Currently, the devices communicate with any other device from the same area with no issue. However, when I ping devices from different areas I receive the error: "Destination host unnreachable" as if I didn't confugure OPSF correctly.

I've check the interfaces, the OSPF protocol and the addresses. Does anyone know what I am missing?

FYI, I'm setting up OSPF using the following commands for example:

Router(config)#router ospf 1
Router(config-router)#network 40.0.0.0 0.255.255.255 area 3
Router(config-router)#exit

And the protocol shows like this in the console:

router ospf 1
 log-adjacency-changes
 network 20.0.0.0 0.255.255.255 area 1
 network 23.0.0.0 0.255.255.255 area 51
 network 26.0.0.0 0.255.255.255 area 51
 network 22.0.0.0 0.255.255.255 area 51
!

I've attached the schematic. Let me know if there is neede further info. Thanks!

[MHM Cisco World · Accepted solution]

You need area0, and all area must have at least one router in this area.

So try change atea 51 into area 0

[Noqqio]

It worked! Thank you so much! Didn't know there must be an area 0

[Joseph W. Doherty]

"Didn't know there must be an area 0"

Yes, it's needed when doing multi-area.  It's the "glue" that connects all the other areas together.

All other areas need to connect to it, so for example having area(1)<>area(0)<>area(2)<>area(3), is invalid for area(3), unless you tie area(3) into area(0) using a "logical" connection when a physical connection cannot be made.

There are other issues when working with multi-area OSPF topologies, which I'm not going to go into.

Lastly, in a situation where you have two (or more) non-zero areas on the same router, that specific router (by default) "knows" those area's routes, but it won't "share" its "known" foreign area topologies with neighboring routers.  I.e. it won't "share" area 1 routes with other area 50 routers, nor the converse.  The sharing is what area zero provides.  (Also there's more to area zero and ABRs [area border routers - i.e. routers that have an area zero and another area, or areas, interfaces], which I'm not going to go into.)