Understanding the ESXi Network IOChain

In this blog post, we go into the trenches of the (Distributed) vSwitch with a focus on vSphere ESXi network IOChain. It is important to understand the core constructs of the vSphere networking layers for i.e. troubleshooting connectivity issues. In a second blog post on this topic, we will look closer into virtual network troubleshoot tooling.

IOChain

The vSphere ESXi network IOChain is a framework that provides the capability to insert functions into the network data-path regardless of the usage of a vSphere Standard Switch (VSS) or a vSphere Distributed Switch (VDS). The IOChain is a group of functions that provides connectivity between ports and the vSwitch. A port has two IOChains based on the direction to and from the vSwitch. Meaning each port in a set is associated with it an input and an output IOChain. This allows for a modular approach by only including optional elements in an IOChain as configured by the user.

Examples of optional elements in an IOChain are VLAN support, NIC teaming, and traffic shaping. Looking at the high-level components in an ESXi network IOChain, we differentiate between the port group, the vSwitch (VSS or VDS) and the uplink level.

Port group level

This is where an optional configured VLAN is interpreted by the VLAN filter, allowing for VLAN dot1q tags for your port group. The security settings Promiscuous mode, MAC address changes, and Forged transmits are also set at the port group level. The user can also optionally configure traffic shaping, either egress only when using a VSS or bi-directional traffic shaping when using a VDS.

vSwitch (VSS or VDS) level

Incoming packets at the vSwitch level are forwarded to their destination using the forwarding engine. Incoming packets at the vSwitch level are forwarded to their destination using the forwarding engine. The forwarding engine contains port information paired with MAC address information. It’s job is to send the traffic to its proper destination. That can be either a VM residing on the same ESXi host or an external host.

The teaming engine is responsible for balancing network packets over the uplink interfaces. The way it does so is depended on the chosen teaming configuration by the user. The traffic shaper module is added to the IOChain if enabled in the port group level.

Uplink level

At this level, the traffic sent from the vSwitch to an external host finds its way to the driver module. This is where all the hardware offloading is taking place. The Supported hardware offloading features depends strongly on the physical NIC in combination with a specific driver module. Typically supported hardware offloading functions that in NICs are TCP Segment Offload (TSO), Large Receive Offload (LRO) or Checksum Offload (CSO). Network overlay protocol offloading like with VXLAN and Geneve, as used in NSX-v and NSX-T respectively, are widely supported on modern NICs.

Next to hardware offloading, the buffer mechanisms come into play in the Uplink level. I.e., when processing a burst of network packets, ring buffers come into play. Finally, the bits transmit onto the DMA controller to be handled by the CPU and physical NIC onwards to the Ethernet fabric.

Standard vSwitch

The following diagram puts all components together to form the IO chain for vSphere networking using a standard vSwitch: (more…)

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vSphere Networking : Bandwidth Reservations

To enforce bandwidth availability, it is possible to reserve a portion of the available uplink bandwidth using Network I/O Control (NIOC). It may be necessary to configure bandwidth reservations to meet business requirements with regards to network resources availability. In the system traffic overview, under the resource allocation option in the Distributed vSwitch settings, you can configure reservations. Reservations are set per system traffic type or per VM.

Strongly depending on your IT architecture, it could make sense to reserve bandwidth for specific business critical workload, vSAN network or IP storage network backend. However, be aware that network bandwidth allocated in a reservation cannot be consumed by other network traffic types. Even when a reservation is not used to the fullest, NIOC does not redistribute the capacity to the bandwidth pool that is accessible to different network traffic types or network resource pools.

Since you cannot overcommit bandwidth reservations by default, it means you should be careful when applying reservations to ensure no bandwidth is gone to waste. Thoroughly think through the minimal amount of reservation that you are required to guarantee for network traffic types.

For NIOC to be able to guarantee bandwidth for all system traffic types, you can only reserve up to 75% of the bandwidth relative to the minimum link speed of the uplink interfaces.

When configuring a reservation, it guarantees network bandwidth for that network traffic type or VM. It is the minimum amount of bandwidth that is accessible. Unlike limits, a network resource can burst beyond the configured value for its bandwidth reservation, as it doesn’t state a maximum consumable amount of bandwidth.

You cannot exceed the value of the maximum reservation allowed. It will always keep aside 25% bandwidth per physical uplink to ensure the basic ESXi network necessities like Management traffic. As seen in the screenshot above, a 10GbE network adapter can only be configured with reservations up to 7.5 Gbit/s.

Bandwidth Reservation Example

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vSphere Networking : Traffic Marking

vSphere network quality control features like the Network I/O Control (NIOC) feature is focused on the virtual networking layer within in a VMware virtual data center. But what about the physical network layer and how the two can cooperate?

In converged infrastructures or enterprise networking environments, Quality of Service (QoS) is commonly configured in the physical network layers. QoS is the ability to provide different priorities to network flows, or to guarantee a certain level of performance to a network flow by using tags. In vSphere 6.7, you have the ability to create flow-based traffic marking policies to mark network flows for QoS.

Quality of Service

vSphere 6.7 supports Class of Service (CoS) and Differentiated Services Code Point (DSCP). Both are QoS mechanisms used to differentiate traffic types to allow for policing network traffic flows.

As related to network technology, CoS is a 3-bit field that is present in an Ethernet frame header when 802.1Q VLAN tagging is present. The field specifies a priority value between 0 and 7, more commonly known as CS0 through CS7, that can be used by quality of service (QoS) disciplines to differentiate and shape/police network traffic. Source: https://en.wikipedia.org/wiki/Class_of_service

One of the main differentiators is that CoS operates at data link layer in an Ethernet based network (layer-2). DSCP operates at the IP network layer (layer-3).

Differentiated services or DiffServ is a computer networking architecture that specifies a simple and scalable mechanism for classifying and managing network traffic and providing quality of service (QoS) on modern IP networks. DiffServ uses a 6-bit differentiated services code point (DSCP) in the 8-bit differentiated services field (DS field) in the IP header for packet classification purposes. Source: https://en.wikipedia.org/wiki/Differentiated_services

When a traffic marking policy is configured for CoS or DSCP, its value is advertised towards the physical layer to create an end-to-end QoS path.

Traffic marking policies are configurable on Distributed port groups or on the DvUplinks. To match certain traffic flows, a traffic qualifier needs to be set. This can be realized using very specific traffic flows with specific IP address and TCP/UDP ports or by using a selected traffic type. The qualifier options are extensive. (more…)

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