EIGRP Routes/SIA

My workplace is planning on moving from an all layer-2 design where layer-2 trunks are used between the core/distribution/access switches to layer-3 design with EIGRP between the core and distribution switches and layer-2 trunks from distribution to access. Routed access is currently not an option.

Here is a little background information about the network. The entire network is broken into zones based on the physical location of groups of devices, each group is usually a few miles apart. Each zone has a fiber connection from the core switch to a single distribution switch and from there multiple access switches are connected to the distribution switch. All end devices are connected to the access switches. I’ll provide more information if needed.

With the layer-2 design, multiple VLANS span across the network via layer 2 trunks and therefore multiple subnets span across the distribution switches. I’ve been asked if I could make this transition work without having to change the IP addressing scheme for the entire network. I was thinking since we are currently using a /16 mask this could be accomplished with the use of a /24 mask.

Our IP addressing convention looks something like this:

10.Vlan.Zone.Host 

Let’s say VLAN 5 currently spans over zone 10, 11, and 12. With the current setup we would have 10.5.0.0/16 reaching all 3 distribution switches over the layer-2 trunk. In the new design we would have 3 new subnets that look like this.

Zone 10 - 10.5.10.0/24 Zone 11 - 10.5.11.0/24 Zone 12 - 10.5.12.0/24 

As it stands we would have no overlapping between them and each distribution switch would have a unique subnet.

My general concern is mostly related with the number of routes the core switch will end up receiving as result of this transition. Each distribution switch will have a neighbor relationship with the core switch (Cisco 6500) and will share between 3 and 5 unique subnets with the core. There are nearly 20 distribution switches and growing so at the minimum there would be 60 EIGRP routes on the core switch. I’m wondering if this would be too demanding for core switch in terms of CPU/Memory.

Secondly, I’ve read some users have issues with EIGRP (SIA) in networks with over 50 routers. Is this something to be thoughtful of before moving forward with the change?

Maybe I’m over thinking this but would rather be sure about this before making with any changes.

Thanks in advance!