Case Study: Two Tier Clos Fabric

The main steps in designing a network infrastructure are as follows:

• Use text and/or diagrams to create an infrastructure description
• Then use the standardized schema to capture the infrastructure description in a machine readable format by doing the following:
  • Add infrastructure device subgraphs using components and links to create edges between components
  • Add infrastructure instances to define the number of devices in a reusable manner
  • Add infrastructure links to define additional information that exists between device instances in the infrastructure
  • Add infrastructure edges between device instances

Infrastructure Description

The following is a diagrammatic and textual description of a generic two tier clos fabric that will be modeled using the standardized schema.

It consists of the following devices:

• 4 generic servers with each server composed of 4 npus and 4 nics with each nic directly connected to one npu via a pcie link. Also every npu in a server is connected to every other npu by an nvlink switch. In addition the server includes a management nic that is separate from test nics.
• 4 leaf switches composed of one asic and 16 ethernet ports
• 3 spine switches composed of one asic and 16 ethernet ports

The above devices will be interconnected in the following manner:

• each leaf switch is connected directly to 1 server and to all spine switches
• every server is connected to a leaf switch at 100 gpbs
• every leaf switch is connected to every spine switch at 400 gpbs

Standardized Definitions

A standardized definition of the preceding two tier clos fabric can be created by following these steps:

• The device is a subgraph which is composed of two components connected to each other using a link.
• It acts as a blueprint allowing for a single definition to be reused multiple times for optimal space complexity.

Create a Server Device

Define a server device based on the infrastructure description.

Server device definition using OpenApiArt generated classes

from infragraph import *

# pyright: reportArgumentType=false


class Server(Device):
    def __init__(self, npu_factor: int = 1):
        """Adds an InfraGraph device to infrastructure based on the following components:
        - 1 cpu for every 2 npus
        - 1 pcie switch for every 1 cpu
        - X npus = npu_factor * 2
        - 1 nic for every npu with 2 nics connected to a pcie switch
        - 1 nvswitch connected to all npus
        """
        super(Device, self).__init__()
        self.name = "server"
        self.description = "A generic server with npu_factor * 4 npu(s)"

        cpu = self.components.add(
            name="cpu",
            description="Generic CPU",
            count=npu_factor,
        )
        cpu.choice = Component.CPU
        npu = self.components.add(
            name="npu",
            description="Generic GPU/NPU",
            count=npu_factor * 2,
        )
        npu.choice = Component.NPU
        nvlsw = self.components.add(
            name="nvlsw",
            description="NVLink Switch",
            count=1,
        )
        nvlsw.choice = Component.SWITCH
        pciesw = self.components.add(
            name="pciesw",
            description="PCI Express Switch Gen 4",
            count=npu_factor,
        )
        pciesw.choice = Component.SWITCH
        nic = self.components.add(
            name="nic",
            description="Generic Nic",
            count=npu_factor * 2,
        )
        nic.choice = Component.NIC
        mgmt = self.components.add(
            name="mgmt",
            description="Mgmt Nic",
            count=1,
        )
        mgmt.custom.type = "mgmt-nic"

        cpu_fabric = self.links.add(name="fabric", description="CPU Fabric")
        nvlink = self.links.add(name="nvlink")
        pcie = self.links.add(name="pcie")

        edge = self.edges.add(scheme=DeviceEdge.ONE2ONE, link=pcie.name)
        edge.ep1.component = mgmt.name
        edge.ep2.component = f"{cpu.name}[0]"

        edge = self.edges.add(scheme=DeviceEdge.MANY2MANY, link=cpu_fabric.name)
        edge.ep1.component = cpu.name
        edge.ep2.component = cpu.name

        edge = self.edges.add(scheme=DeviceEdge.MANY2MANY, link=nvlink.name)
        edge.ep1.component = npu.name
        edge.ep2.component = nvlsw.name

        for idx in range(pciesw.count):
            edge = self.edges.add(scheme=DeviceEdge.MANY2MANY, link=pcie.name)
            edge.ep1.component = f"{cpu.name}[{idx}]"
            edge.ep2.component = f"{pciesw.name}[{idx}]"

        npu_slices = [f"{idx}:{idx+2}" for idx in range(0, npu.count, 2)]
        for npu_idx, pciesw_idx in zip(npu_slices, range(pciesw.count)):
            edge = self.edges.add(scheme=DeviceEdge.MANY2MANY, link=pcie.name)
            edge.ep1.component = f"{npu.name}[{npu_idx}]"
            edge.ep2.component = f"{pciesw.name}[{pciesw_idx}]"

        for nic_idx, pciesw_idx in zip(npu_slices, range(pciesw.count)):
            edge = self.edges.add(scheme=DeviceEdge.MANY2MANY, link=pcie.name)
            edge.ep1.component = f"{nic.name}[{nic_idx}]"
            edge.ep2.component = f"{pciesw.name}[{pciesw_idx}]"


if __name__ == "__main__":
    device = Server(npu_factor=2)
    device.validate()
    print(device.serialize(encoding=Device.YAML))

Server device definition as yaml

components:
- choice: cpu
  count: 1
  description: Generic CPU
  name: cpu
- choice: npu
  count: 2
  description: Generic GPU/NPU
  name: npu
- choice: switch
  count: 1
  description: NVLink Switch
  name: nvlsw
- choice: switch
  count: 1
  description: PCI Express Switch Gen 4
  name: pciesw
- choice: nic
  count: 2
  description: Generic Nic
  name: nic
- choice: custom
  count: 1
  custom:
    type: mgmt-nic
  description: Mgmt Nic
  name: mgmt
description: A generic server with npu_factor * 4 npu(s)
edges:
- ep1:
    component: mgmt
  ep2:
    component: cpu[0]
  link: pcie
  scheme: one2one
- ep1:
    component: cpu
  ep2:
    component: cpu
  link: fabric
  scheme: many2many
- ep1:
    component: npu
  ep2:
    component: nvlsw
  link: nvlink
  scheme: many2many
- ep1:
    component: cpu[0]
  ep2:
    component: pciesw[0]
  link: pcie
  scheme: many2many
- ep1:
    component: npu[0:2]
  ep2:
    component: pciesw[0]
  link: pcie
  scheme: many2many
- ep1:
    component: nic[0:2]
  ep2:
    component: pciesw[0]
  link: pcie
  scheme: many2many
links:
- description: CPU Fabric
  name: fabric
- name: nvlink
- name: pcie
name: server

Create a Switch Device

Define a switch device based on the infrastructure description.

Switch device definition using OpenApiArt generated classes

from infragraph import *

# pyright: reportArgumentType=false


class Switch(Device):
    def __init__(self, port_count: int = 16):
        """Adds an InfraGraph device to infrastructure based on the following components:
        - 1 generic asic
        - nic_count number of ports
        - integrated circuitry connecting ports to asic
        """
        super(Device, self).__init__()
        self.name = "switch"
        self.description = "A generic switch"

        asic = self.components.add(
            name="asic",
            description="Generic ASIC",
            count=1,
        )
        asic.choice = Component.CPU
        port = self.components.add(
            name="port",
            description="Generic port",
            count=port_count,
        )
        port.choice = Component.PORT

        ic = self.links.add(name="ic", description="Generic integrated circuitry")

        edge = self.edges.add(scheme=DeviceEdge.MANY2MANY, link=ic.name)
        edge.ep1.component = asic.name
        edge.ep2.component = port.name


if __name__ == "__main__":
    device = Switch()
    print(device.serialize(encoding=Device.YAML))

Switch device definition as yaml

components:
- choice: cpu
  count: 1
  description: Generic ASIC
  name: asic
- choice: port
  count: 16
  description: Generic port
  name: port
description: A generic switch
edges:
- ep1:
    component: asic
  ep2:
    component: port
  link: ic
  scheme: many2many
links:
- description: Generic integrated circuitry
  name: ic
name: switch

Create an Infrastructure of Instances of devices, Links and Edges

Define an infrastructure based on the infrastructure description.

Two Tier Clos Fabric Infrastructure using OpenApiArt generated classes

from infragraph import *
from infragraph.server import Server
from infragraph.switch import Switch
from infragraph.infragraph_service import InfraGraphService


class ClosFabric(Infrastructure):
    """Return a 2 tier clos fabric with the following characteristics:
    - 4 generic servers
    - each generic server with 2 npus and 2 nics
    - 4 leaf switches each with 16 ports
    - 3 spine switch each with 16 ports
    - connectivity between servers and leaf switches is 100G
    - connectivity between servers and spine switch is 400G
    """

    def __init__(self):
        super().__init__(name="closfabric", description="2 Tier Clos Fabric")

        server = Server()
        switch = Switch()
        self.devices.append(server).append(switch)

        hosts = self.instances.add(name="host", device=server.name, count=4)
        leaf_switches = self.instances.add(name="leafsw", device=switch.name, count=4)
        spine_switches = self.instances.add(name="spinesw", device=switch.name, count=3)

        leaf_link = self.links.add(
            name="leaf-link",
            description="Link characteristics for connectivity between servers and leaf switches",
        )
        leaf_link.physical.bandwidth.gigabits_per_second = 100
        spine_link = self.links.add(
            name="spine-link",
            description="Link characteristics for connectivity between leaf switches and spine switches",
        )
        spine_link.physical.bandwidth.gigabits_per_second = 400

        host_component = InfraGraphService.get_component(server, Component.NIC)
        switch_component = InfraGraphService.get_component(switch, Component.PORT)

        # link each host to one leaf switch
        for idx in range(hosts.count):
            edge = self.edges.add(scheme=InfrastructureEdge.ONE2ONE, link=leaf_link.name)
            edge.ep1.instance = f"{hosts.name}[{idx}]"
            edge.ep1.component = host_component.name
            edge.ep2.instance = f"{leaf_switches.name}[{idx}]"
            edge.ep2.component = switch_component.name

        # link every leaf switch to every spine switch
        print()
        for leaf_idx in range(leaf_switches.count):
            for spine_idx in range(spine_switches.count):
                edge = self.edges.add(scheme=InfrastructureEdge.ONE2ONE, link=spine_link.name)
                edge.ep1.instance = f"{leaf_switches.name}[{leaf_idx}]"
                edge.ep1.component = f"{switch_component.name}[{host_component.count + spine_idx}]"
                edge.ep2.instance = f"{spine_switches.name}[{spine_idx}]"
                edge.ep2.component = f"{switch_component.name}[{leaf_idx}]"

ClosFabric infrastructure definition as yaml

description: 2 Tier Clos Fabric
devices:
- components:
  - choice: cpu
    count: 1
    description: Generic CPU
    name: cpu
  - choice: npu
    count: 2
    description: Generic GPU/NPU
    name: npu
  - choice: switch
    count: 1
    description: NVLink Switch
    name: nvlsw
  - choice: switch
    count: 1
    description: PCI Express Switch Gen 4
    name: pciesw
  - choice: nic
    count: 2
    description: Generic Nic
    name: nic
  - choice: custom
    count: 1
    custom:
      type: mgmt-nic
    description: Mgmt Nic
    name: mgmt
  description: A generic server with npu_factor * 4 npu(s)
  edges:
  - ep1:
      component: mgmt
    ep2:
      component: cpu[0]
    link: pcie
    scheme: one2one
  - ep1:
      component: cpu
    ep2:
      component: cpu
    link: fabric
    scheme: many2many
  - ep1:
      component: npu
    ep2:
      component: nvlsw
    link: nvlink
    scheme: many2many
  - ep1:
      component: cpu[0]
    ep2:
      component: pciesw[0]
    link: pcie
    scheme: many2many
  - ep1:
      component: npu[0:2]
    ep2:
      component: pciesw[0]
    link: pcie
    scheme: many2many
  - ep1:
      component: nic[0:2]
    ep2:
      component: pciesw[0]
    link: pcie
    scheme: many2many
  links:
  - description: CPU Fabric
    name: fabric
  - name: nvlink
  - name: pcie
  name: server
- components:
  - choice: cpu
    count: 1
    description: Generic ASIC
    name: asic
  - choice: port
    count: 16
    description: Generic port
    name: port
  description: A generic switch
  edges:
  - ep1:
      component: asic
    ep2:
      component: port
    link: ic
    scheme: many2many
  links:
  - description: Generic integrated circuitry
    name: ic
  name: switch
edges:
- ep1:
    component: nic
    instance: host[0]
  ep2:
    component: port
    instance: leafsw[0]
  link: leaf-link
  scheme: one2one
- ep1:
    component: nic
    instance: host[1]
  ep2:
    component: port
    instance: leafsw[1]
  link: leaf-link
  scheme: one2one
- ep1:
    component: nic
    instance: host[2]
  ep2:
    component: port
    instance: leafsw[2]
  link: leaf-link
  scheme: one2one
- ep1:
    component: nic
    instance: host[3]
  ep2:
    component: port
    instance: leafsw[3]
  link: leaf-link
  scheme: one2one
- ep1:
    component: port[2]
    instance: leafsw[0]
  ep2:
    component: port[0]
    instance: spinesw[0]
  link: spine-link
  scheme: one2one
- ep1:
    component: port[3]
    instance: leafsw[0]
  ep2:
    component: port[0]
    instance: spinesw[1]
  link: spine-link
  scheme: one2one
- ep1:
    component: port[4]
    instance: leafsw[0]
  ep2:
    component: port[0]
    instance: spinesw[2]
  link: spine-link
  scheme: one2one
- ep1:
    component: port[2]
    instance: leafsw[1]
  ep2:
    component: port[1]
    instance: spinesw[0]
  link: spine-link
  scheme: one2one
- ep1:
    component: port[3]
    instance: leafsw[1]
  ep2:
    component: port[1]
    instance: spinesw[1]
  link: spine-link
  scheme: one2one
- ep1:
    component: port[4]
    instance: leafsw[1]
  ep2:
    component: port[1]
    instance: spinesw[2]
  link: spine-link
  scheme: one2one
- ep1:
    component: port[2]
    instance: leafsw[2]
  ep2:
    component: port[2]
    instance: spinesw[0]
  link: spine-link
  scheme: one2one
- ep1:
    component: port[3]
    instance: leafsw[2]
  ep2:
    component: port[2]
    instance: spinesw[1]
  link: spine-link
  scheme: one2one
- ep1:
    component: port[4]
    instance: leafsw[2]
  ep2:
    component: port[2]
    instance: spinesw[2]
  link: spine-link
  scheme: one2one
- ep1:
    component: port[2]
    instance: leafsw[3]
  ep2:
    component: port[3]
    instance: spinesw[0]
  link: spine-link
  scheme: one2one
- ep1:
    component: port[3]
    instance: leafsw[3]
  ep2:
    component: port[3]
    instance: spinesw[1]
  link: spine-link
  scheme: one2one
- ep1:
    component: port[4]
    instance: leafsw[3]
  ep2:
    component: port[3]
    instance: spinesw[2]
  link: spine-link
  scheme: one2one
instances:
- count: 4
  device: server
  name: host
- count: 4
  device: switch
  name: leafsw
- count: 3
  device: switch
  name: spinesw
links:
- description: Link characteristics for connectivity between servers and leaf switches
  name: leaf-link
  physical:
    bandwidth:
      choice: gigabits_per_second
      gigabits_per_second: 100
- description: Link characteristics for connectivity between leaf switches and spine
    switches
  name: spine-link
  physical:
    bandwidth:
      choice: gigabits_per_second
      gigabits_per_second: 400
name: closfabric