Multiple ABR for the same area.

m.gamal · ‎12-22-2002

i have an OSPF network with 3 normal areas and of course a backbone area( area 0)

and one router that resides in area (2) is connected by two links to two ABR routers that connects area (2) to area (0).

i tried to draw a diagram for the topology , R1 is connected to Internet and the Ethernet is in area(0), R2 and R3 are ABRs.

R4 is a remote site and having two links (T1)links to the each for ABR.

also R5 is a remote site and is connected to one of the ABRs by T1.and Link 3 is in area (2) also

note: tha ABRs are on ethernet segment.

when link 2 is not connected, traffic from internet destined to R4 is through link 2 traffic from internet destined toR5 is throught Link3

when i connect link 2 i thought that traffic destined for R4 will be load shared on link1 and link 2 , but this doesn't happen.

what happends is that all traffic destined for R4 comes throught link1 only. and traffic destined to R5 comes throught link1 then link 2 ..and doesn't go throught link 3 at all

can anyone help me in this problem., knowing that link cost are known..

Thanks

Mhaddad

R1

____________|___Ethernet_____________

| |

R2 R3.

, , ,

Link 1 , , Link 2 , Link 3

, , ,

R4 R5

lgijssel · ‎12-22-2002

Are R4 and R5 interconnected on the Ethernetside?

I assumed that they are not.

Looks like you have a static route connected to link1 that takes precedence over the rest. More info will be nescearry though.

Can you upload a sh ip route from R2 and from R4?

m.gamal · ‎12-22-2002

no ..R4 and R5 are not connected to the ethernet..

and i am not having static routes.., the problem is that i tried to draw a shematic diagram..but when i posted my message..it changed..

so if i can send u the diagram by any other mean..this will make the vision clear for you...if i can send it by mail ..u will see the toplogy well.

and the sho ip route will be too long..

deilert · ‎12-23-2002

It is hard to diagnose with the information given . Do not forget that in OSPF will prefer in interarea router over in interarea route even if the interarea route has a cheaper cost .

cdileepyadav@gmail.com · ‎07-24-2018

can we have two ABRs in the network?

Yes, we can have. Having one ABR is like a single point of failure. So, it's better to have two ABRs for redundancy purpose. But, we need to use in a proper way other wise suboptimal routing may happen.

Refer the below link for better understanding:

https://community.cisco.com/t5/routing/ospf-problem-with-two-abr/td-p/2086740

cdileepyadav@gmail.com · ‎07-24-2018

can we have two ABRs in the network?

Yes, we can have. Having one ABR is like a single point of failure. So, it's better to have two ABR for redundancy purpose. But, we need to use in a proper way otherwise sub-optimal routing may happen.

Refer the below link for better understanding:

https://community.cisco.com/t5/routing/ospf-problem-with-two-abr/td-p/2086740