NCN Networking

Non-compute nodes (NCNs) and compute nodes (CNs) have different network interfaces used for booting; this topic focuses on the network interfaces for management NCNs.

NCN network interfaces

The following table includes information about the different NCN network interfaces:

Name Type MTU
mgmt0 Slot 1 on the SMNET card 9000
mgmt1 Slot 2 on the SMNET card or slot 1 on the second SMNET card 9000
bond0 LACP link aggregate of mgmt0 and mgmt1, or mgmt0 and mgmt2 on dual-bonds (when bond1 is present) 9000
bond1 LACP link aggregate of mgmt1 and mgmt3 9000
lan0 Externally facing interface 1500
lan1 Another externally facing interface, or anything (unused) 1500
hsn0 High-Speed Network interface 9000
hsnN+1 Another high-speed network interface 9000
vlan002 Virtual LAN for managing nodes 1500
vlan004 Virtual LAN for managing hardware 1500
vlan007 Virtual LAN for the Customer Access Network 1500

These interfaces can be observed on an NCN with the following command.

ncn# ip link

Device naming

The underlying naming relies on biosdevname. This helps conform device naming into a smaller set of possible names. It also helps reveal when driver issues occur; if an administrator observes an interface with name that does not conform to this naming scheme, then this is an indication of a problem.

The MAC-based udev rules set the interfaces during initial boot in iPXE. When a node boots, iPXE will dump the PCI buses and sort network interfaces into 3 buckets:

  • mgmt: internal/management network connection
  • hsn: high-speed connection
  • lan: external/site connection

The source code for the rule generation is in metal-ipxe. Continue reading for technical information on the PCI configuration/reading.

Vendor and bus ID identification

The initial boot of an NCN sets interface udev rules because it has no discovery method yet.

The information needed is:

  • PCI Vendor IDs for devices/cards to be used on the Management network.
  • PCI Device IDs for the devices/cards to be used on the High-Speed Network.

The 16-bit vendor ID is allocated by the PCI-SIG (Peripheral Component Interconnect Special Interest Group).

The information belongs to the first 4 bytes of the PCI header, and administrators can obtain it by reading the PCI bus (for example, by using the lspci command).

ncn# lspci | grep -i ethernet
ncn# lspci | grep c6:00.0

The device and vendor IDs are used in iPXE for bootstrapping the nodes. This allows generators to swap IDs out for certain systems until smarter logic can be added to cloud-init.

The following table includes popular vendor and device IDs.

The numbers in bold are the defaults in metal-ipxe’s boot script.

Vendor Model Device ID Vendor ID
Intel Corporation Ethernet Connection X722 37d2 8086
Intel Corporation 82576 1526 8086
Mellanox Technologies ConnectX-4 1013 15b3
Mellanox Technologies ConnectX-5 1017 15b3
Giga-Byte Intel Corporation I350 1521 8086
QLogic Corporation FastLinQ QL41000 8070 1077