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.”