Hello Alex! Thanks for answering! Well...my purpose is to migrate (some of) the SVIs - exactly as they currently are - from one Core (a standalone switch) to another one (a VSX Cluster) thus without changing any IP addresses.
Let me say I have various 10.100.x.0 /24 network segments routed by the standalone Aruba 5400R zl2 switch.
Each network segment is tied to a specific VLAN id with a SVI so, as example, 10.100.0.0 /24 has VLAN 1000 with 10.100.0.254 as its Gateway, 10.100.1.0 /24 has VLAN 1001 with 10.100.1.254 as its Gateway...and so on...up to, say, the latest network segment 10.100.255.0 /24 associated to VLAN 1255 and 10.100.255.254 as its Gateway.
Let me suppose I need to move some of the SVIs (not all, just a subset of them) into a new Router R2 directly connected (L2) to the current Router R1: I'll need a mechanism to transfer - example - the routing of the VLAN 1100 network segment 10.100.100.0 /24 (which owns the SVI 10.100.100.254) from the Aruba 5400R zl2 standalone switch to the VSX Cluster and this, among many other things, will imply that the 10.100.100.254 Gateway IP address - which needs to remain the very same during and after the transfer (No DHCP in those specific DC network portion) - will pass under the control of the VSX Cluster (with Active Gateway enabled configured with the SVI address set to 10.100.100.254 and each VSX Member configured with a reserved IP address such as the 10.100.100.251 associated to VSX Primary and the 10.100.100.252 associated to VSX Secondary for that VLAN) leaving the control of the Aruba 5400R zl2.
All the above remembering that R2 currently isn't routing and it is just a Layer 2 extension of the R1.
To simplify the whole picture I can say that the R1 (Aruba 5400R zl2) shall remain the Router of - let me say - all network segments belonging to the main root 10.100.0.0 /16 network while the R1 (VSX Cluster) shall become the Router of - let me say - all network segments belonging to the main root 10.200.0.0 /16 network BUT, actually, both those main root networks (with all their numerous /24 segments) are routed only by R1.
The reality is a little bit more complex because there isn't a straight distinction between the two main root networks (the routing of some /24 segments belonging of the first main root network needs to be transferred to R2 too) and so I should take care about each /24 segment almost individually.
From the PoV of the clients (edge devices and server systems) insisting on those /24 network segments the used approach should be the one providing the least possible disruption time or no disruption at all (if possible).
To clarify I'm speaking about dividing (the routing of) a DC Network which is currently serving DC+Campus assets into a DC Network serving the routing of DC systems and a Campus Network serving the routing of Campus edge devices...and the assets I can work with are (and are limited to) (a) the R1 Aruba 5400R zl2, (b) the Aruba 8360 VSX Cluster that will become the future R2 Router and (c) a Perimeter Firewall which is - actually - the NHG Next Hop Gateway for RoW configured as the Router of last resort on the R1...and, in between, it should also take care of becoming the NHG for the next-to-come Router R2 (I know there is a lot more behind and around to discuss about...but my very first doubt is how to partly migrate the routing duties).