networking - Datacenter ISP wants to assign an IP range to an existing ip address that we already use

I have a question about the setup of our data center regarding a new IP range.

The situation is as follows.

we own/use a range x.x.x.x/28 we got it already from our data center.
we have 16 addresses we already use for our servers (13 actually without network, broadcast and default gateway)

Now we want to order another range y.y.y.y/27 that has 32-3 usable addresses I presume.

Because they cannot assign this range to the same network port where x.x.x.x/28 is assigned to, they ask me for an ip address within the x.x.x.x/28 range, let's say a.a.a.a. to route the new range (y.y.y.y/27) to.

The other solution is to hire a new network port to which the y.y.y.y/27 range can be routed through normally.

My account manager is a bit vague and we can't afford to switch data center right now.

So my question is;

how do I configure this?
does a.a.a.a become the default gateway somehow? I can't get a clear apprehension of how this technically should work. Is there a special name for this type of routing? Google doesn't give me any clear answers, because I don't know exactly what I'm looking for.

I hope someone can shine a light for me on this one.

Thx

Bram

Answer

Your server which has a.a.a.a address assigned will receive traffic addressed to network y.y.y.y/27. You can assign addresses from the y.y.y.y/27 range as an IP aliases on the same network interface as a.a.a.a by using ip addr add y.y.y.y dev eth0 or you can route them to other servers by using ip route add y.y.y.y via a.a.a.x (a.a.a.x is a different server from range x.x.x.x/28)