On overlay networks, NSX-T supports routing of inter-VLAN traffic on an L3 domain. During routing, virtual distributed router (VDR) uses VLAN ID to route packets between VLAN subnets.

Inter-VLAN routing overcomes the limitation of 10 vNICs that can be used per VM. NSX-T supporting inter-VLAN routing ensures that many VLAN subinterfaces can be created on the vNIC and consumed for different networking services. For example, one vNIC of a VM can be divided into several subinterfaces. Each subinterface belongs to a subnet, which can host a networking service such as SNMP or DHCP. With Inter-VLAN routing, for example, a subinterface on VLAN-10 can reach a subinterface on VLAN-10 or any other VLAN.

Each vNIC on a VM is connected to the N-VDS through the parent logical port, which manages untagged packets.

To create a subinterface, on the Enhanced N-VDS switch, create a child port using the API with an associated VIF using the API call described in the procedure. The subinterface tagged with a VLAN ID is associated to a new logical switch, for example, VLAN10 is attached to logical switch LS-VLAN-10. All subinterfaces of VLAN10 have to be attached to LS-VLAN-10. This 1–1 mapping between the VLAN ID of the subinterface and its associated logical switch is an important prerequisite. For example, adding a child port with VLAN20 to logical switch LS-VLAN-10 mapped to VLAN-10 makes routing of packets between VLANs non-functional. Such configuration errors make the inter-VLAN routing non-functional.

Prerequisites

  • Before you associate a VLAN subinterface to a logical switch, ensure that the logical switch does not have any other associations with another VLAN subinterface. If there is a mismatch, inter-VLAN routing on overlay networks might not work.

  • Ensure that hosts run ESXi v 6.7 U2 or later versions.

Procedure

  1. To create subinterfaces for a vNIC, ensure that the vNIC is updated to a parent port. Make the following REST API call. 

    PUT https://<nsx-mgr-ip>/api/v1/logical-ports/<Logical-Port UUID-of-the-vNIC>
{
  "resource_type" : "LogicalPort",
  "display_name" : "parentport",
  "attachment" : {
    "attachment_type" : "VIF",
    "context" : {
      "resource_type" : "VifAttachmentContext",
      "vif_type": "PARENT"
    },
    "id" : "<Attachment UUID of the vNIC>"   
  },
  "admin_state" : "UP",
  "logical_switch_id" : "UUID of Logical Switch to which the vNIC is connected",  
  "_revision" : 0
}
  2. To create child ports for a parent vNIC port on the N-VDS that is associated to the subinterfaces on a VM, make the API call. Before making the API call, verify that a logical switch exists to connect child ports with the subinterfaces on the VM. 
    POST https://<nsx-mgr-ip>/api/v1/logical-ports/
{
  "resource_type" : "LogicalPort",
  "display_name" : "<Name of the Child PORT>",   
  "attachment" : {
    "attachment_type" : "VIF",
    "context" : {
      "resource_type" : "VifAttachmentContext",
      "parent_vif_id" : "<UUID of the PARENT port from Step 1>",     
      "traffic_tag" : <VLAN ID>,    
      "app_id" : "<ID of the attachment>",  ==> display id(can give any string). Must be unique.
      "vif_type" : "CHILD"
    },
   "id" : "<ID of the CHILD port>"  
  },
  
  "logical_switch_id" : "<UUID of the Logical switch(not the PARENT PORT's logical switch) to which Child port would be connected to>",         
  "address_bindings" : [ { "mac_address" : "<vNIC MAC address>", "ip_address" : "<IP address to the corresponding VLAN>", "vlan" : <VLAN ID> } ],       
  "admin_state" : "UP"
}

Results

NSX-T Data Center creates subinterfaces on VMs.