Virtual Cloud Network (VCN)

Introduction 

• Virtual Cloud Network (VCN) lives within an OCI region (not AD level, a regional component)
• OCI VCN support ranges from 10.0.0.0/16 (highest) to 10.0.0.0/30 (lowest) only.
• VCN reserves the first two IP addresses and the last one in each subnet CDIR
• When you create a VCN, you give it an address space which is a range of IP addresses that you assign. Example 10.0.0.0/16 which is a range from 10.0.0.0 to 10.0.255.255 (/16 reservers the first 16 bits for the network)
• VCN covers a single contiguous CIDR block and the allowed size range is /16 to /30
• Network bandwidth: depends on service compute shape

Default VCN Components

The following default components cannot be deleted but can change the contents

• Default Security List
• Default Routing Table
• Default DHCP

Subnets

• Continuous range
• Cannot overlap
• Can be defined on AD level or Regional (span all ADs)
• Instances are placed on subnets and get their IP addresses and network configuration from the subnet.
• The first host address (0) is reserved for the network
• The last address (255) is reserved for broadcast
• Types
• Private subnets: only private IP addresses assigned to instances VNICs
• Public subnets:  contains both private and public IP addresses.
• Address ranges examples
• 10.0.0.0/16         10.0.0.0 - 10.0.255.255
• 10.0.0.0/24          10.0.0.0-10.0.0.255
• 10.0.0.0/27          10.0.0.0-10.0.0.31
• 10.0.0.0/32           one address 10.0.0.0 
• 0.0.0.0/0              Any IP address

VNIC

• Virtual Network Interface Card
• Attached to a compute instance
• Each instance can have two or more VNICs, each VNIC can have multiple private and public IP addresses.
• The primary private IP address is mandatory
• One compute instance could have VNIC in different subnets or even different VCNs

IP Addresses

Private IP Addresses

• A primary private IP address is mandatory, created when an instance is created.
• Can have up to 31 additional secondary IPs.
• Secondary VNIC address can be on different subnets or VCNs

Public IP Addresses

• Reachable from the internet
• Optional on instances
• Multiple IPs are possible for an instance (each public ip assigned to one VNIC).
• Two kinds:
• Ephemeral: 
• Temporary and exist for the life of the instance
• Can be assigned one per VNIC
• Reserved: 
• Persistent and existing beyond the life of the instance. Can be unassigned and reassigned to other instances.
• Can be assigned to max 32
• No charge for using Public IP
• Cannot choose or edit

Routing Table

• Contains rules about how IP packets can travel to different IP addresses out of the VCN.
• Attached to subnets
• Each subnet uses a single routing table, which can be changed later.
• Consist of a set of route rules, each rule specify 
• Destination CIDR block
• Route target -- the next hop -- for the traffic that matches the destination CIDR 
• Contain rules about how IP packets can travel to different IP addresses outside the VCN.
• The routing table is used only if the destination IP address is not within the VCN CIDR block.
• No routing rules are required to enable traffic within the VCN.