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OSPF Inter-Area Routing

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sclebo05

Technical User
Oct 7, 2009
4
US
Hello all,

I have 3 sites, each with a Class B within them. Currently 2 sites are live and connected, Corporate Hub being Area 0 and spoke A being Area 1. My goal is to turn up a third site spoke B, and have all 3 sites connected via ospf/gre/ipsec point to point links, a triangle. As expected, traffic between Spoke A and Spoke B route through the hub, as he is Area 0. I would rather this be a last resort, and would like to find a way to 'short circuit' traffic between the spokes for expediency, and fall back to the hub if they lose contact with each other. As OSPF is behaving as it should, I need to find an alternative or re-engineer OSPF.

Playing with GNS3, I was actually able to do this with RIP between the 2 remote sites, with a lower administrative distance and no summarization, but it felt silly to run multiple IGPs. I've thought about turning up a second OSPF process and doing some filtering on redistribution, but that also seemed overly complicated. Since the sites are class Bs, I've thought about using static routes between the spokes for simplicity.

Ultimately, I'd like each leg of the triangle to be used at all times. Failover would be nice, but is not necessary. Is my design crazy/incorrect? Without a shared network (Frame Relay, MPLS, etc) between the sites, how to people generally do this?

Summary of the sites:

Corporate Hub 10.10.0.0/16 Area 0.0.0.0
Spoke A 10.20.0.0/16 Area 1.1.1.1
Spoke B 10.30.0.0/16 Area 2.2.2.2

I'm looking more for conceptual solutions than exact config. If it matters, I'm ACTUALLY using Fortigate 310B firewalls, which provide me with OSPF, RIP, and Static routing as possible tools. If I get it working in my Cisco lab, I can adapt it to my production gear.
 
How big is your routing table? Why not just make everything Area 0 or least your WAN/VPN routers have their WAN links in Area 0 and the LAN networks in there own Area?

Andy
 
I agree with Andy. The tunnel interfaces on each device should be backbone/Area 0 and the internal interfaces of each spoke site should be in their own standard area

I hate all Uppercase... I don't want my groups to seem angry at me all the time! =)
- ColdFlame (vbscript forum)
 
That might work. Would be be recommended to keep the 'core' at the Corporate HQ in area 0 as well?
 
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