NSX-T Logical Routing

In NSX-T Data Center, a logical router consists of two components:

Distributed router (DR)
Services router (SR)

Distributed Router (DR)

A DR is essentially a router with logical interfaces (LIFs) connected to multiple subnets. It runs as a kernel module and is distributed in hypervisors [ESXi/KVM] across all transport nodes, including Edge nodes. When a logical router is created through NSX-T Manager or the API, the management plane validates and stores configuration. It then pushes this configuration via the Rabbit MQ message bus to the CCP nodes, which in turn push this configuration to the LCPs on all the transport nodes. A DR instance is instantiated as a kernel module.

End-to-end Communication Flow for Management, Control, and Data Planes

Services Router:

East-west routing is completely distributed in the hypervisor, with each hypervisor in the transport zone running a DR in its kernel. However, some facets of NSX-T are not distributed,
including:

Physical infrastructure connectivity
NAT
DHCP server
Metadata Proxy for OpenStack
Edge Firewall

A services router (SR) – also referred to as a services component – is instantiated when a service is enabled that cannot be distributed on a logical router.

The Service Router on an NSX Edge is only instantiated in the following scenarios:

When the uplink port is configured Tier-0 Logical Router for the Physical network connectivity
When NAT is enabled on the Tier-0 logical Router, etc

The logical router contains the following interfaces:

Uplink– Interface connecting to the physical infrastructure/router. Static routing and eBGP are supported on this interface.
Downlink – Interface connecting to a logical switch.
Intra-Tier Transit Link – Internal link between the DR and SR. This link along with logical switch prefixed with “transit-bp” is created automatically and defaults to an IP address in 169.254.0.0/28 subnet. The address range may be changed if it is used somewhere else in the network.

Types of Logical Routers:

NSX-T supports a multi-tiered routing model with logical separation between provider router function provided by Tier-0 Logical Router and tenant routing function by the Tier-1 Logical Router. The concept of multi-tenancy is built into the routing model.

In NSX-T an admin can create two different type of logical routers