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 NetworkManager is disabled on Charon-SSP OCI. Therefore, the interface configuration relies on ifcfg-files in /etc/sysconfig/network-scripts.

 The information in this chapter is not comprehensive. Please refer to the Oracle cloud documentation for up-to-date and comprehensive information.

Concepts

VCN: VCN stands for Virtual Cloud Network. Before you can launch an instance, you need to have a virtual cloud network (VCN) and subnet into which you can launch the instance. A VCN is associated with resources such as a CIDR address block, a route table, an Internet gateway, a default security list, etc.

Subnet: A subnet is a subdivision of the VCN. The subnet directs traffic according to a route table. For example, if you access the instance via a public IP address, the route table will direct traffic to an Internet gateway. A subnet also uses a security list to control traffic in and out of the instance.

Instance: An instance is a virtual machine that is launched into a VCN and subnet. It is associated with an image (e.g., Charon-SSP image) and a certain shape representing the virtual hardware.

VNIC: A virtual network interface card, which attaches to an instance and resides in a subnet to enable a connection to the subnet's VCN. The VNIC determines how the instance connects with endpoints inside and outside the VCN. Each instance has a primary VNIC that's created during instance launch and cannot be removed. All VNICs of an instance must be in the same availability domain as the instance.

Address Assignment

Each VCN is assigned a block of private IP addresses. This block can be split by the user to form several IP subnets. Routing within one VCN works automatically.

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• it is automatically assigned a private IP address from the address range assigned to the subnet,
• the user can choose whether to assign a public IP address if the subnet is a public subnet.

 Public IP addresses are not directly visible to the instance. The instance operating system always works with the private address. For external connections, the private address is mapped to the public IP address via NAT.

Reserved addresses (important, if manual address assignment is used):

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• 10.1.1.0: the network address
• 10.1.1.1: reserved by OCI for the default router
• 10.1.1.255: network broadcast address.

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Other special addresses:

• 169.254.0.0/16: Reserved for OCI use.

Public IP addresses:

There are two types of public IP addresses (only available in public subnets):

• Ephemeral addresses:
  • maximum one per VNIC,
  • assigned by Oracle,
  • persistent during the lifetime of the associated private IP address,
  • can only be associated with the primary private IP address of a VNIC,
  • a user can only delete it but not associate it with a different private IP address.
• Reserved addresses:  
  • maximum 32 per VNIC,
  • created and assigned by the user,
  • can be re-assigned to a different private IP,
  • can be associated with primary and secondary private IP addresses,
  • exists until the user deletes it.

Host to Guest Communication Considerations

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