Network Planning

A clustered resource depends on a cluster network. This network can be either persistent (it is always “up” even after provisioning) or temporary, only used for provisioning and/or out of band system control and management (e.g., IPMI).

The cluster network must be dedicated to the cluster because Warewulf uses network services (particularly DHCP) which may conflict with services on another mixed-use network. A dedicated cluster network is also important for security, as the cluster network often has an implicit level of trust associated with it.

The Warewulf server is often “dual homed,” meaning that it has separate network interfaces connected to each of the cluster network and an external network. But it is also possible for the cluster network to be routable from other, more general-purpose networks.

Many clusters have more than one internal network. This is common for performance critical HPC clusters that implement a high speed and low latency network like InfiniBand. In this case, this network is used for high speed data transfers for inter-process communication between compute nodes and file system IO.

Warewulf will need to be configured to use the private cluster management network. Warewulf will use this network for booting the nodes over PXE. There are three network protocols used to accomplish this DHCP/BOOT, TFTP, and HTTP on port 9873. Warewulf will use the operating system’s provided version of DHCP (ISC-DHCP) and TFTP for the PXE bootstrap to iPXE, and then iPXE will use Warewulf’s internal HTTP services to transfer the larger files for provisioning.

Addressing

The addressing scheme of your private cluster network is 100% up to the system integrator, but for large clusters, many organizations like to organize the address allocations. Below is a recommended IP addressing scheme which we will use for the rest of this document.

  • 10.0.0.1: Private network address IP

  • 255.255.252.0: Private network subnet mask (10.0.0.0/22)

Here is an example of how the cluster’s address can be divided for a 255 node cluster:

  • 10.0.0.1 - 10.0.0.255: Cluster infrastructure including this host, schedulers, file systems, routers, switches, etc.

  • 10.0.1.1 - 10.0.1.255: DHCP range for booting nodes

  • 10.0.2.1 - 10.0.2.255: Static node addresses

  • 10.0.3.1 - 10.0.3.255: IPMI and/or out of band addresses for the compute nodes