I have 2 6500 working as core and ospf area 0 running between them. These 2 core switches are connected to each other with a single link. There are 2 4500 distribution switches connected to these 2 cores having 2 links to each of the core. We have defined static routes to different subnets on 4500 so that if one subnet on one 4500 wants to reach another subnet on 2nd 4500 then it will go to core and then it will come back on another 4500 where that subnet resides as there is no direct link between these 2 4500 switches.
We have given 2 static routes for each subnet so that both the core can forward the traffic to another 4500. Now
when link between 2 cores goes down then half of the traffic is dropped as 4500 is not able to know that link between 2 core is down.
Even with all of the link redundancy, unfortunately this will happen every time.
When two routes to the same destination with equal administrative distance exist, the router will load balance. Even if the link to the specified next hop doesn't exist the router will continue to forward packets using both routes. This is the nature of static routing.
If static routing isn't a requirement I recommend adding the 4500s to the OSPF area. OSPF has the ability to route around link failures.
Are the 4500s used as L2 devices only? If so, the subnets should be terminated on the core devices, right? In which case these subnets could be learnt vi OSPF. Why do you need static routes? I think I don't really understand your topology. Can you provide us with a bit more information.
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