Scenario: Backbone Area OSPF Tuning, Multiple OSPF Processes

[va1bhav32768]

Hi,

Scenario:

My topology diagram is attached. Please note the following:

1. Branch_1 & Branch_2 have Three connections:

   1. MPLS/BGP Link to Head Office.

   2. ISDN to repective Regional Offices. Running OSPF. Regional Office is an ABR. Branch's ISDN are in area 1 and area 2 respectively
   3. VSAT connection over OSPF/GRE Tunnel (running in area 0) to Head Office.
      
      
2. So, basically when connection 1 and 2 are down, the branch runs on GRE/VSAT link and connects to DC/HO in Area 0.
3. Problem: Due to very flappy nature of VSAT link, the backbone OSPF Process/Area 0 at DC Core router is constantly recalculating. Being in Area 0, these VSAT connected links receive entire routing table which is an overkill for a low bandwidth, high latency link. The adjacencey/convergence takes 5-10 minutes to come up!

Diagram:

Config:

For example, Branch_1 router interfaces would look something like this:

F0/0 -- LAN -- ip address/24 -- OSPF Area 1

F0/1 -- VSAT Device -- ip address/29 (non-routed)

S0/0 -- MPLS/BGP -- ip address/30

BRI0/0 -- ISDN Line

Dialer 1 -- ISDN to Regional Office (RO) -- ipaddress/30 -- OSPF Area 1

Dialer 2 -- ISDN to Head Office (HO/DC) -- ipaddress/30 -- OSPF Area 0

Tunnel 1 -- GRE Tunnel running over VSAT to Head Office (HO/DC) -- ipaddress/30 -- OSPF Area 0

The branch basically becomes a stub node when both link 1 & 2 are down (MPLS and ISDN).

Goal: My goal is to tune OSPF on the VSAT link in such a way that minimal routing traffic is sent and the OSPF converges very quickly.

Options worth exploring: I have few solutions that I plan to try , but, I want to double sure on the design part and also future issues that may occur.

1. NSSA Totally Stubby: Put all the interfaces (f0/0, Dialer, Tunnel) of the branch in a New OSPF Area (eg. Area 500) and configure the Area as NSSA Totally Stubby at the HO/DC Core Router. This will help cut down the routing info and converge faster. However, this is not feasible since we need to Dial ISDN (Dialer 1) to Regional Office etc.
   
   Also, reverse routes will be needed to DC/HO router for the other interfaces of the Branch router.
   
   
2. Default/Static Routing: Don't want, messy, unmanageable, IP scheme of all those branches are different. We have around 400 links on VSAT.
3. Two OSPF Processes: Create two OSPF processes on HO/DC Core Router. Now the Main process will hold all the information about rest of the network and the new OSPF process will handle only VSAT GRE links. We can redistribute the main OSPF into new one and filter/summarize things. Unclear about this, need to lab it.
4. Run BGP: Can't and won't do. Design and complexity issues.
5. ?

Thats all I could come up with. What will be the best method to solve this matter? Looking for some suggestions. Please let me know if more insight or details are needed.

--TIA

Added few more things...

[va1bhav32768]

Option #5: Put a new router between HO/DC Core Router to act as an ABR. Now put all the VSAT GREs in a new Area 500. Make it a NSSA or originate default route or something clever. However, problem would be getting a new router with enough power, the Backhaul link termination on the new router etc.