OSPF with dual ABR's: which area should the trunk use.

[p.buitelaar]

Hi,

I have the following setup:

In each site I have two Cat4506's in a specific ospf area.

Switch A is connected to primary data center.

Switch B is connected to secondary data center.

All links from the different sites to the primary- and secondary data center are in area 0.

The two data centers are interconnected in area 0.

In which area should the trunk between the two cat4506's in the sites be placed? In area 0 or in the site specific area?

In each site a few vlan's are deployed, with spt and hsrp pointing to the switch A.

thanks and regards, Pieter-Jon Buitelaar

[Harold Ritter]

The best would be to have two VLANs between the two ABRs. One configured in area 0 and the other in the site specific area.

This would provide optimal routing.

Hope this helps,

[p.buitelaar]

That's interesting, I did not think about that option.

Can you explain why?

Thank you!

[Harold Ritter]

This would ensure that this high speed transit link shows as an intra-area route in both areas and that optimal routing is achieved.

Hope this helps,

[gibsthomas]

Do u happen to have a diagram??

[gibsthomas]

I would go with what hritter said. you should trunk between same area that traffic stays in the same area. and you may also truck the backbone area (0) for redunadancy