Subnet size for a VLAN in a Cisco network running OpenStack:

  • /24 (255.255.255.0) → 254 usable IPs (Common choice for small to medium setups)

  • Scalable but not excessive for proof of concept.

  • Keeps network simple while allowing enough IPs for VMs and infrastructure.

  • /22 (255.255.252.0) → 1022 usable IPs (Better for larger deployments)

  • Avoids unnecessary complexity of larger subnet masks like /22

  • /21 (255.255.248.0) → 2046 usable IPs (For even larger networks)

More Proof:

VLAN configuration guidance on your Cisco switches for OpenStack:

  • VLAN 100 is used for OpenStack instances.

  • VLAN 200 is used for OpenStack management.

  • VLAN 300 is for storage traffic (if needed).

  • Trunking is used to allow multiple VLANs between switches and OpenStack nodes.

Number of IP addresses required for OpenStack on Cisco:

  • OpenStack Controller needs 1-2 ips

  • Compute Nodes needs 3 ips

  • Management VLAN (VLAN 200) → For OpenStack services (Controller, Compute, Storage).

  • Instance VLAN (VLAN 100) → For VM traffic.

  • Storage VLAN (VLAN 300) → If using Ceph/NFS.

  • External VLAN → If you need external internet access for VMs.