CentOS 8.x Cloudstack 4.15 Networking

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Once cloudstack is deployed as per CentOS 8.x Cloudstack 4.15 Initial zone setup with VLANs, we need to create "Guest networks" for VMs. There are following types of networks:

Isolated

These networks use a VLAN from the VLAN range specified during zone setup. We need to specify IP subnet, gateway and subnet mask. The cloudstack router will use a available VLAN and the gateway IP would be assigned to router. All other machines will communicate with outside world only via this router. The VMs in isolated network will get IP from cloudstack router DHCP.

After network is created we need to go network and then "Egress Rules" tab to allow outgoing traffic from this isolated network to outside world.

If we want to make an isolated VM accessible from outside then we need to go corresponding network and go to public IP addresses tab. We need to use and existing public IP already assigned to this isolated network or "+Acquire New IP". Then click on the IP address for configuring both Firewall and "Port forwarding" to enable access to a isolated VM via this public IP. Note that just port forwarding is not enough. We need to allow the ports in firewall for communication to work.

Note that isolated networks are specific to a cloudstack domain (tenant) and not shared between domains (Tenants)

Shared

Shared networks are used when there is an existing L3 switch based (or some other device based) gateway in external network in a particular VLAN. In such cases cloudstack router does not takes gateway IP. It assumes that given gateway is available in the specified VLAN for external communication. However, cloudstack will try to assign IPs specified with IPv4 start IP and IPv4 end IP range to the VMs using its DHCP from cloudstack router. Thus, gateway functionality comes from external network but DHCP is provided by cloudstack router.

In such cases we go to shared network and then go to virtual routers tab. Click on router and then go to "Health checks" tab to ensure that network is working as expected.

There is no public IP or firewall or egress rule configuration in such networks.

Such networks can be shared between multiple cloudstack domains (Tenants)

L2

L2 networks are similar to shared networks but even more simplified. In this case there is no router at all from cloudstack and hence all functionality such as DHCP, DNS, etc. is provided by external network resources. Cloudstack only ensures that VM gets connected to VLAN specified.

Note that by default you may not get option to specify VLAN. Change the network offering type to "DefaultL2NetworkOfferingVlan" to get option to specify VLAN ID.

Such networks can be shared between multiple cloudstack domains (Tenants)

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