Advice

[Tareq Emad Al Asfoor]

Hello, 

I have network that have two ABR ... These ABR connected with Area 0 from one side and with Area 50 from another side .. I activated Totally Stubby Areas in this network ... My question is,  here i will have two ABR which one will inject default route to the Stub area ? and how i can control it ?

Many Thanks 

[paul driver]

Hello

I am not sure i understand you topology -  TSSA ABR wll indeed inject a default into the the stub area

Are you asking how to negate the injection fo this default?

1) On a specific rtr within the stub area you can try something like this:

ip prefix-list nodefault seq 5 deny 0.0.0.0/0
ip prefix-list nodefault seq 10 permit 0.0.0.0/0 le 32

router ospf x
distribute-list prefix nodefault in


2) For all Rtrs in the stub area -  on the ABR

router ospf xx
max-metric router-lsa summary-lsa 16777215


Lastly, I guess the above examples defeats the object of having a TSSA in the first place


res

Paul

[Tareq Emad Al Asfoor]

Hi , 

I attached here picture to my topology .. When i acteive the Totally stub area on the two ABR which one will inject the defult route to area 50 ? can i decided which one will inject the defult route like change cost or like this  .. and how the Totally stub area idea will work in like this topology ? 

Thanks 

[Richard Burts]

If you have a totally stub area and there are two ABR for that totally stub area then I believe that both ABR will inject a default route into the area.

HTH

Rick

[Tareq Emad Al Asfoor]

Thanks for your replay .. But this will not cause problem ? and in my topology that i attached it,  the two ABR conected with area 50 from side and connected to area 0 from another side .. IS this will not cause any problem 

[Richard Burts · Accepted solution]

Perhaps I do not understand something about the topology that you suggest. Why would you expect there to be a problem?

A router in a totally stub area has a very small set of OSPF routes (limited to routes within that area) and needs a default route to be able to get to an ABR and to the backbone where the more extensive set of routes exist. If there are two ABR and if both connect to the backbone then why would it matter which ABR the interior router uses to get to the backbone?

HTH

Rick

[Joseph W. Doherty · Accepted solution]

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Posting

As Rick has noted, traffic could flow out either ABR (and back in via either ABR).  I.e. asymetrical routing is possible, but this shouldn't normally cause an issue.

That said, one situation you can run into, if your two ABRs don't share a direct link (doesn't have to be physical), if either loses its connection to area zero (if I remember correctly), the default injection is not withdrawn for a stub ABR.  So, the ABR with the lost area zero connection will try to route to the other ABR, but without a direct connection, "in-between" routers could route back to that ABR creating a routing loop.

Your diagram shows a direct (area 50?) connection between ABRs, but it wouldn't hurt to backstop that with a GRE tunnel (area 5) between the two ABRs.

[Richard Burts]

I am glad that our answers were helpful. Thank you for using the rating system to mark this question as answered. This will help other readers in the forum to identify discussions that have helpful information.

HTH

Rick

[paul driver]

Hello

In that toplogy your traffic should route with the two defauts

R3-R5_R1_R6
R7-R4_R2_R6

However lets say you apply the max-metric router-lsa  to  R2 then the stub routers

will take the the default via R1

res
Paul