The DLR is optimised for forwarding in the logical space between VMs, on VXLAN-backed or VLAN-backed portgroups.

The DLR has the following properties:

  • High performance, low overhead first-hop routing:

  • Scales linearly with the number of hosts

  • Supports 8-way ECMP on uplink

  • Up to 1,000 DLR instances per host

  • Up to 999 logical interfaces (LIFs) on each DLR (8 x uplink + 991 internal) + 1 x management

  • Up to 10,000 LIFs per host distributed across all DLR instances (not enforced by NSX Manager)

Keep in mind the following caveats:

  • Cannot connect more than one DLR to any given VLAN or VXLAN.

  • Cannot run more than one routing protocol on each DLR.

  • If OSPF is used, cannot run it on more than one DLR uplink.

  • To route between VXLAN and VLAN, the transport zone must span single DVS.

The DLR’s design at a high level is analogous to a modular router chassis, in the following ways:

  • ESXi hosts are like line cards:

    • They have ports with connected end stations (VMs).

    • This is where the forwarding decisions are made.

  • The DLR Control VM is like a Route Processor Engine:

    • It runs dynamic routing protocols to exchange routing information with the rest of the network.

    • It computes forwarding tables for “line cards” based on the configuration of interfaces, static routes, and dynamic routing information.

    • It programs these forwarding tables into the “line cards” (via the Controller Cluster, to enable scale and resiliency).

  • The physical network connecting ESXi hosts together is like a backplane:

    • It carries VLAN-encapsulated or VXLAN-encapsulated data between the “line cards.”