This section provides an overview of workload traffic flows using HCX Network Extension with and without Mobility Optimized Networking.

Mobility Optimized Networking Terminology

The following definitions apply when discussing HCX MON.

Flat Network

A network design approach where the topology is flattened to simplify configuration and administration. Flat networks with large broadcast domains are contrary in principle to segmented networks, which restrict broadcast domains and relies on VLANs, subnets and routers.

Segmented (Hierarchical) Network

A network design approach where the topology is segmented using variable length subnetting and VLANs to create a hierarchical routing configuration. Segmented, or hierarchical networks have controlled broadcast domains and are contrary in principle to flat networks, which rely on large broadcast domains and ARP discovery.

Network Latency

A measure of delay for data to go from the source server to the destination over a network

Round-Trip Time / Delay

The length time it takes for a signal to be sent to a destination, plus the time it takes for the acknowledgement to be received.

Use Cases for Mobility Optimized Networking

Mobility Optimized Networking improves routed connectivity patterns for multi-segment applications and virtual machines with inter-VLAN dependencies as those virtual machines are migrated into the cloud.

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Without MON, HCX Network Extension expands the on-premises broadcast domain to the cloud SDDC while the first hop routing function remains at the source. The network tromboning effect is observed when virtual machines connected to different extended segments communicate.

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MON optimization enables migrated virtual machines to reach segments within the SDDC.

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Mobility Optimized Networking can be configured to allow migrated virtual machines to reach services hosted within a public cloud.

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Mobility Optimized Networking enables migrated virtual machines to use the SDDC Internet interface (with SNAT).

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Mobility Optimized Networking Outcomes by Migration Type

  • HCX Bulk migrated virtual machines are automatically MON optimized in the SDDC.

  • HCX vMotion migrated virtual machines use the on-premises gateway until they are specifically configured to use the cloud gateway in the MON interface.

  • HCX RAV migrated virtual machines use the on-premises gateway until they are specifically configured to use the cloud gateway in the MON interface.

  • Virtual machines created in the segment prior to enabling the MON feature use the on-premises gateway until they are specifically configured to use the cloud gateway in the MON interface.

Mobility Optimized Networking Operation

Network Extension with HCX Mobility Optimized Networking provides the following functionality:

  • Select or deselect Mobility Optimized Networking at the time of stretching a network

  • Select or deselect MON for already extended networks

  • Select or deselect MON on an individual VM basis for VMs residing on extended networks in the SDDC

  • Display which VMs are using Mobility Optimized Networking.

  • When using HCX to vMotion a VM, preserve existing network connections while providing an option to activate Mobility Optimized Networking on that VM after migration

  • Configure MON Route Policy to define on-premises (non-SDDC) subnets or exception/deny subnets for local egress.

The following process explains what happens during the various phases of Mobility Optimized Networking.

  1. Mobility Optimized Neworking is enabled for an HCX extended segment.

    HCX enables the network ID (gateway IP) in the SDDC Compute Gateway. It is enabled with a limited /32 255.255.255.255 network mask.

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  2. Static routes are added in the SDDC Compute Gateway for migrated virtual machines on HCX extended network.

    HCX adds reachability information for the migrated virtual machine (in the form of a virtual machine specific static route) to the SDDC Compute Gateway, allowing reachability within the SDDC. This vm static route is not advertised to the on-premises environment. The HCX L2 path is used to reach subnets not in the SDDC.

  3. Using SDDC forwarding technology, the virtual machine uses the SDDC Compute Gateway to reach the SDDC networks.

For reachability outside of the SDDC tier-1, the MON policy configuration is evaluated according to the MON policy configuration. Matching subnets are sent to the original premises router. Nonmatched subnets are sent to the SDDC tier-0 router. For more information on MON policy routes, see Mobility Optimized Networking Policy Routes.