OSPF multi area adjacency

[sachin30720041]

Hello, 

I am trying to understand multi-area adjacency.

r1----area0----r2

|.                        |

|                         |

area0.              area0

|                         |

|                         |

r3-----area1--r4

R3's loopback:- 3.3..3.3 in area0

r4's loopback :-4.4.4.4.4 in area0

r3's routing table points to r1 to go to r4's loopback(4.4.4.4). while low cost path is available but inter-area route. So I configured multi-area adjacency on r3 and r4.

r3's gi0/0 pointing towards r4.

int gi0/0

ip ospf network point-to-point

ip ospf 1 area 1

ip ospf multi-area 1

r4's gi0/0 pointing towards r3.

int gi0/0

ip ospf network point-to-point

ip ospf 1 area 1

ip ospf multi-area 1

But still in R3's routing points to R1 for 4.4.4.4.

R3's routing table should point to r4. correct?

Is there any problem with the config?

Thanks,

Sachin

[balaji.bandi]

You can view the OSPF database and routing output why that chose over the connected interface.

here is a good example and explanation :

https://blog.ine.com/2011/04/04/understanding-ospf-external-route-path-selection

[pman]

in your case: R3 learned 4.4.4.4 through Intra-Area (O) (R1>R2>R4)

ospf path selection rules:

Intra-Area (O)
Inter-Area (O IA)
External Type 1 (E1)
External Type 2 (E2)
NSSA Type 1 (N1)
NSSA Type 2 (N2)

Inter-Area (O IA) IA is less preferred than Intra-Area (O) so I think R3 would prefer an inrta-area (O) path over an inter-Area (O IA)

[Giuseppe Larosa · Accepted solution]

Hello @sachin30720041 ,

you have attempted to configure multi area adjacency on link between R3 and R4.

have a look at the folowing document

https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/118879-configure-ospf-00.html#anc15

Compare your configuration with the following one:

interface Ethernet0/1
ip address 192.168.23.2 255.255.255.0
ip ospf network point-to-point
 ip ospf multi-area 99
ip ospf 1 area 0
end

Your configuration should be:

nt gi0/0

ip ospf network point-to-point

ip ospf 1 area 0

ip ospf multi-area 1

on both routers

With your current config there is no multi area the link is only in area 1 and as noted by other O routes are preferred over O IA regarldess of metric.

Hope to help

Giuseppe