Turning flat network into a routing network (Still very green)

Good morning!

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Edit: If possible, how would i do it? It made sense in my CCNA training because of Routers with serial cables but, i can't figure it out for the life of me between buildings.

TLDR: Long story short, Is this possible 172.18.0.0/22 ? Visually it makes sense but i know very little of architecture and still green.

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I am new to this sub and looking for advice how to turn my flat network into a routing network. I recently got my CCNA R&S back in march. Still very green when it comes to networking but i am trying!

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I'm a sys admin at my job and trying to improve my corporate network. We had a contractor come out last year and assist but i was never apart of the conversation and don't understand why/what he did what he did because of lack of documentation and other issues.

He broke up some buildings into a 10.0.0.0/24 network by putting them into VLANS

"interface Vlan138

ip address 10.38.0.1 255.255.255.0

ip helper-address *dhcp server*

!

!

router eigrp 1

network 172.18.0.0 0.0.3.255

redistribute connected

!

ip default-gateway *IP ADDRESS*

ip route 0.0.0.0 0.0.0.0 *ip default-gateway* "

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Even though he put these buildings into VLANS, the "core" routers with vlan 1 ip address is still in the same network (broadcast) (I.E 0.1,0.2,0.3 etc).

Also the static route gets pushed back to the default gateway no matter what L3 switch i am in.

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All my "core" routers in separate buildings are L3 and are cisco. By seeing this "router eigrp 1 network 172.18.0.0 0.0.3.255" and doing a bunch of cdp neighbors, i finally have a lay out 172.18.0.0/22 .

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My end goal is to have this broken out and be able to use the extra sub networks as test units, Guest/work WIFI networks etc