Cisco APIC Layer 3 Networking Configuration Guide, Release 6.2(x)

Cisco ACI configuration for microsoft NLB servers

Updated: April 17, 2026

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Describes the deployment considerations and configuration requirements for Microsoft NLB servers within the fabric. It outlines the transition from Layer 2-only support to Layer 3 gateway capabilities starting in release 4.1.

Microsoft NLB deployment involves integrating load-balanced server clusters into the fabric using specific bridge domain and EPG configurations.

Support for Unicast, Multicast, and IGMP modes.
Requirement for specific bridge domain settings including unknown unicast flooding.
Integration of VIP subnets and MAC address handling within EPGs.

Deployment modes and configuration options

The following table summarizes the deployment considerations for each Microsoft NLB deployment mode.

Table 1. Cisco ACI Deployment Modes with Microsoft NLB
Deployment Mode	Unicast Mode	Multicast Mode	IGMP Mode
Cisco ACI as a Layer 2 Network, With External Router as Layer 3 Gateway	Supported on leaf switch models with -EX, -FX, -FX2 or -FX3 at the end of the switch name.	Supported on leaf switch models with -EX, -FX, -FX2 or -FX3 at the end of the switch name, as well as leaf switch models that do not have a suffix at the end of the switch name.	Supported on leaf switch models with -EX, -FX, -FX2 or -FX3 at the end of the switch name, as well as leaf switch models that do not have a suffix at the end of the switch name. However, Microsoft NLB traffic is not scoped by IGMP, but rather is flooded instead.
Cisco ACI as a Layer 3 Gateway	Supported on release 4.1 and later.	Supported on release 4.1 and later.	Supported on release 4.1 and later.

General configuration tasks

Beginning with release 4.1, configuring the fabric to connect Microsoft NLB servers consists of the following general tasks:

Configuring the VRF in egress or ingress mode.
Configuring a bridge domain (BD) for the Microsoft NLB servers, with L2 unknown unicast in flooding mode and not in hardware-proxy mode.
Defining an EPG for all the Microsoft NLB servers that share the same VIP and associating it with the BD.
Entering the Microsoft NLB VIP as a subnet under the EPG.
Configuring a contract between the Microsoft NLB EPG (provider) and the client EPG (consumer).

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