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Addressing and Connectivity Overview

This diagram shows elements of a Calico network in a simplified way that allows us to focus on how IP addresses are assigned to workloads, and whether and how workloads have connectivity to and from the Internet (as well as to other workloads within the data center).

Network provisioning and IP addresses

In current Calico, the ranges from which IP addresses may be assigned to workloads are all provisioned by the data center operator. These ranges are all shared, in the sense that IP addresses from them might be allocated to workloads for different tenants, and the overall IPv4 and IPv6 address spaces are ‘flat’, in that any IPv4 address can in principle - meaning subject to security policy - communicate with any other IPv4 address, and similarly for IPv6.

Within the shared address spaces there may be ranges of IP addresses (both v4 and v6) that are routable from outside the data center. Other shared network IP address ranges will not be routable from outside: they are potentially accessible from all other workloads within the data center, but not from the Internet. This is all under the control of the data center operators, as it is they who provision the shared network.

Outbound and inbound connectivity to and from the Internet

Subject to security configuration, all forms of IP addressing can initiate outbound connections to outside the data center. In the IPv4 case, the border gateway must NAT the source address of outbound packets, so that responses to them are routed back to the data center.

In the diagram above, 10.65/16 and 2001:db8:a41:2/64 are IPv4 and IPv6 subnets that are not routable from outside the data center, and 102.25.78/24 and 2001:cf2:45:1/64 are subnets that are routable from outside. For a workload to be accessible from outside the data center, it simply needs one of its vNICs to be given an IP address from one of the externally routable ranges.

The following table summarizes the properties of the IP addresses in the diagram.

IP address Routable from Internet? Can access Internet?
10.65.0.18 No Yes
2001:db8:a41:2::12 No Yes
102.25.78.2 Yes Yes
2001:cf2:45:1::3a Yes Yes