Networking Overview

A VCN covers one or more IPv4 CIDR blocks or IPv6 prefixes of your choice. The allowable VCN size range is
/16
to /30. Example: 10.0.0.0/16. The Networking service reserves the first two IP
addresses and the last one in each subnet’s CIDR.
You can enable IPv6 for
your VCNs when you create them, or you can enable IPv6 on existing IPv4-only VCNs. If
you decide to use an Oracle-allocated IPv6 prefix, you always receive a /56.
Alternately, you can import your own BYOIP IPv6 prefix
from which you can assign any prefix of /64 or larger to a VCN, or you can assign a ULA
prefix of /64 or larger. GUA ranges can be up to 2000::/3 and ULA ranges can be up to
fc00::/7. IPv6 subnets are always /64 in size.

For your VCN,
Oracle recommends using the private IP address ranges specified in RFC 1918 (the RFC recommends 10.0/8 or 172.16/12 but Oracle doesn’t
support those sizes so use 10.0/16, 172.16/16, and 192.168/16). However, you can
use a publicly routable range. Regardless,
this documentation uses the term private IP address when referring to IP
addresses in your VCN’s CIDR. Address ranges that are disallowed are described in IP Addresses Reserved for Use by Oracle. For
IPv6-enabled VCNs, Oracle can either allocate a global unicast address /56 prefix or you
can create a VCN with a BYOIPv6 prefix.

The
VCN’s
CIDR blocks must not overlap with each other, with CIDRs in your
on-premises network, or with the CIDRs of another
VCN you peer with. The subnets in a given VCN must not overlap with each
other. For reference, here’s a CIDR calculator.

IPv6 addressing is supported for all commercial and government regions. For more
information, see IPv6 Addresses.