Does Oracle RAC require that the Ethernet aliases be in a different IP range than the base addresses? Let's say I have 3 nodes running RAC. The base addresses (eth0 interfaces) for those nodes are in the 192.168.1.0/24 range.

From what I've seen RAC requires that you create Ethernet alias interfaces (eth0:0) on each node, with addresses in a different range. But is that a requirement? Isn't it possible to create eth0:0 with just other addresses within 192.168.1.0/24?
From what I've seen RAC requires that you create Ethernet alias
  interfaces (eth0:0) on each node, with addresses in a different range.


Thats not correct. If eth0 is the interface for the public network, then the VIPs and SCAN VIPs must be on the same subnet, that is exactly what you are asking for. Also its not you, but Oracle Grid Infrastructure that creates and manages these virtual IPs, you just specify the name and address for them.

Furthermore, the private virtual IPs (called HAIP) on the private network (lets say eth1) will be created in the 169.254.0.0/16 subnet, no matter what.

So here is a sample configuration for a 3 node cluster:

Public addresses:

node1, eth0: 192.168.1.1/24
node2, eth0: 192.168.1.2/24
node3, eth0: 192.168.1.3/24


VIPs, with names defined in DNS or hosts file:

node1-vip, eth0:0: 192.168.1.11/24
node2-vip, eth0:0: 192.168.1.12/24
node3-vip, eth0:0: 192.168.1.13/24


Private addresses (note the different subnet), names are not necessary to be defined:

node1-priv, eth1: 192.168.2.1/24
node2-priv, eth1: 192.168.2.2/24
node3-priv, eth1: 192.168.2.3/24


SCAN VIPs (11.2.0.1 or above), with one single name defined in DNS:

192.168.1.21/24
192.168.1.22/24
192.168.1.23/24


Can run on any node as eth0:X. Number of SCAN VIPs is independent of number of nodes.

HAIP (11.2.0.2 or above), no names, the IPs are dynamic, so I have just put some random IPs here to complete the example:

node1: eth1.1: 169.254.190.49/16
node2: eth1.1: 169.254.203.17/16
node3: eth1.1: 169.254.243.66/16