Layer 3 Data Center using BGP with subnet overlap


Hi Experts,

I am currently working with a client to revamp their data center. They are currently using Cisco 6500 switches. I am planning to propose them a layer 3 network but there is one thing i dont understand. If customer has overlapping subnets across the racks, how can we manage that using layer 3 bgp/ospf between leaf and spine? (routing on the host is not an option here since customer is too cisco focused).

Since this is a revamp we cannot go with a big bang approach from day 1 by advising them to keep one subnet per rack. How does layer 3 design works with overlapping subnets between racks?

3 replies

Userlevel 4
How many racks does a subnet need to exist on? How many racks are their total and how many spines / distribution seitches do you have?
I will be gathering this info but just for my info does it matter?. Since its a legacy network i am expecting lot of overlap, same subnet existing across multiple racks. We are planning to have ToR switches for every rack so any idea how to get it working?
Userlevel 4
If a subnet is just 2 racks depending on server density you can just use MLAG to cover 2 racks. If you only have something like 6 Racks and two spines you might as well just do MLAG all the way to the exit. If you have more than 2 spines or lots and lots of racks it make sense to do network virtualization like LNV or EVPN (I prefer the latter).

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