Understanding Domain Types in Cisco ACI - External Bridge domains vs Fibre Channel Domains Vs L3 Domains Vs Physical Domains

 

Understanding Domain Types in Cisco ACI

Cisco ACI (Application Centric Infrastructure) provides a flexible and scalable network architecture. One of the key components in ACI is the concept of domains, which define how endpoints and external networks interact with the fabric. In this blog, we will explore four important domain types in Cisco ACI: External Bridge Domains, Fibre Channel Domains, L3 Domains, and Physical Domains. Understanding their roles and use cases is essential for designing robust ACI environments.

1. External Bridge Domains - Not Recommended

External Bridge Domains are used to extend Layer 2 connectivity beyond the ACI fabric. They are typically associated with L2Out configurations and allow external devices to participate in the same broadcast domain as internal ACI endpoints. This is useful for integrating legacy Layer 2 networks or extending VLANs to external switches.

2. Fibre Channel Domains

Fibre Channel (FC) Domains are designed for integrating ACI with storage area networks (SANs). These domains support Fibre Channel over Ethernet (FCoE) or native Fibre Channel protocols. They enable zoning and connectivity to storage arrays and are essential for environments that require high-performance storage access through Cisco MDS switches or similar infrastructure.

3. L3 Domains

L3 Domains are used for establishing Layer 3 routed connectivity to external networks. They are associated with L3Out configurations and support dynamic routing protocols such as OSPF and BGP, as well as static routes. L3 Domains are crucial for connecting the ACI fabric to the internet, WANs, or other routed domains.

4. Physical Domains

Physical Domains are used to connect bare-metal servers and non-virtualized devices to the ACI fabric. They are associated with AAEPs (Attachable Access Entity Profiles) and interface policies. Physical Domains typically use static VLAN pools and are ideal for environments where VLANs are manually assigned to interfaces for direct server or appliance connectivity.

Summary Comparison Table

Domain Type	Purpose	Associated With	Typical Use Case
External Bridge Domain	Extend Layer 2 outside ACI	L2Out	Legacy VLAN bridging, external switches
Fibre Channel Domain	SAN connectivity	FCoE, FC zoning	Storage integration (e.g., MDS, SAN arrays)
L3 Domain	Routed external connectivity	L3Out	Internet, WAN, external routing
Physical Domain	Connect physical devices to ACI	AAEP, Interface Profiles	Bare-metal servers, appliances