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Query on OSPF area for DR site

Hello,

Our existing DR site is set to same area as Data center (area 0). IP address scheme is different than DC. We are planning to move this DR to new location. Iam thinking of set up the new site in different area than backbaone. We will be having direct p2p gig link connectivity between two sites. Will that be ok or cause any issues?

TIA

MS

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: Query on OSPF area for DR site

Hello,

Without knowing more detail about your network topology, we can give you only general answers.

Areas in OSPF should be deployed if you are planning to do at least one of the following optimizations:

  • Summarize networks
  • Limit or filter the amount of unnecessary routing information
  • Reduce the size/complexity of the link-state database
  • Contain the scope of propagation of topology changes

Creating areas just for the sake of having the routing domains partitioned into areas is generally not necessary. It shall be noted that in OSPF, simply partitioning the network into several areas does not result into loss of reachability. All networks and destinations will remain reachable, only perhaps suboptimal routing can occur (packets taking a longer route than necessary) - this strongly depends on the topology and on the area borders. So in this point of view, there are no issues to consider.

Personally, I suggest that instead of looking whether creating an area creates an issue, you should try to analyze if there is a compelling reason to create another area. If there is then create it - I do not expect any outstanding issues to come. However, if there is no special reason to create another OSPF area, I would probably just suggest remaining in a single-area configuration which is generally simpler and perhaps somewhat easier to maintain and troubleshoot.

Best regards,

Peter

5 REPLIES
Cisco Employee

Re: Query on OSPF area for DR site

Hello,

Without knowing more detail about your network topology, we can give you only general answers.

Areas in OSPF should be deployed if you are planning to do at least one of the following optimizations:

  • Summarize networks
  • Limit or filter the amount of unnecessary routing information
  • Reduce the size/complexity of the link-state database
  • Contain the scope of propagation of topology changes

Creating areas just for the sake of having the routing domains partitioned into areas is generally not necessary. It shall be noted that in OSPF, simply partitioning the network into several areas does not result into loss of reachability. All networks and destinations will remain reachable, only perhaps suboptimal routing can occur (packets taking a longer route than necessary) - this strongly depends on the topology and on the area borders. So in this point of view, there are no issues to consider.

Personally, I suggest that instead of looking whether creating an area creates an issue, you should try to analyze if there is a compelling reason to create another area. If there is then create it - I do not expect any outstanding issues to come. However, if there is no special reason to create another OSPF area, I would probably just suggest remaining in a single-area configuration which is generally simpler and perhaps somewhat easier to maintain and troubleshoot.

Best regards,

Peter

Re: Query on OSPF area for DR site

In addition... I have another location which is aready set as different area (I inherited this n/w setup).

So...

Loc#A : Area 10 --> Gig/OSPF --> Loc#B : Area 0 (BB area) --> Gig/OSPF -->  Loc#C : Area 5 (New DR).

Now in future, we have plans to get gig link from Loc#A --> Loc#C (new DR) for redundancy purpose.

So, in that scenario, Loc#A may reach Loc#C, directly than via Backbone. Will that be an issue...? (ie traffic between areas not passing via BB).

TIA

MS

Re: Query on OSPF area for DR site

Any suggestions?

TIA

MS

Hall of Fame Super Silver

Re: Query on OSPF area for DR site

MS

Yes that is likely to create an issue. You do not tell us whether there is more than 1 router at locA and a locC. If there is only a single router in locA and only a single router in locC then this can work. But if there is more than one router in a loc then only the router that has the extra link will forward traffic over that link. The second router in the area will continue to forward all of its traffic to remote areas through the backbone.

I would suggest that it is much better to have both the primary DC and the DR DC in area 0.

HTH

Rick

Re: Query on OSPF area for DR site

Thanks Rick. I guess I need to keep the DR as area 0, to avoid further issues when we complete all migrations. I have attached rough visio diagram for current (upcoming decos in 'dotted') and final setup. Please suggest any recomeded changes- I prefer to use EIGRP, but as I inherited with lot of OSPF configs in place , I will let it go that way for now. Also, no summary being used on the any routers.

Tanks

MS

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