Two ABRs between two OSPF areas for redundancy

[Kaushik Ray]

Hello

I would like to know if it is possible to put two ABRs between two OSPF areas for redundancy purposes. I am just new to OSPF and would be grateful if someone can share their views on this or pass on any document which explains advantages and disadvantages of such a setup.

Many Thanks in advance

[JohnTylerPearce · Accepted solution]

Yes this is completely possible.You mainly do this load balancing and redundancy


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[JohnTylerPearce]

Just remember the costs will run the same way, as with only one ABR, but with one exception if the ABRs are connected by non backbone links they will prefer the most direct path to Area O always.


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[Richard Burts · Accepted solution]

There are some resources that suggest that to simplify OSPF that you have only a single ABR per area. And some discussions of OSPF stub and totally stub suggest having a single ABR for an OSPF area. I do not agree with these. I believe that any OSPF area with a single ABR is an OSPF area with a significant single point of failure. I advocate that OSPF area should have at least two ABR.

HTH

Rick

[Joseph W. Doherty]

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Posting

As noted by the other, yes it's possible.  And agreeing with Rick, having only a single ABR creates a single point of failure.

Disadvantages include need for additional ABRs and the "gotchas" that you can run into.  With a single ABR, there's only a single ingress/egress point for the area, but with multiple ABRs, then you have all the issues related to which will be used.  It's very easy to fall into suboptimal path selection.

[Kaushik Ray]

Thanks everyone for your thoughts on this. I was trying to find some documents regarding this as well. Can you please share the link as well if you have one in hand?

Regards