Describes how Layer 3 outside network configurations manage traffic flow between the Cisco ACI fabric and external networks, including route discovery, quality-of-service selection, and traffic forwarding.
A Layer 3 outside network configuration (L3Out) defines how traffic is forwarded between the fabric and external networks.
Discovers addresses of external network nodes.
Selects routes and quality of service.
Forwards traffic that enters, exits, or transits the fabric.
Layer 3 outside connection references
Refer to the following resources for configuration details and connection types.
For guidelines and cautions for configuring and maintaining Layer 3 outside connections, refer to DEC guidelines and limitations.
Layer 3 Out for routed connectivity to external networks
A Layer 3 Out enables routed connectivity to external networks by associating a fabric access external routed domain with a tenant Layer 3 external instance profile for a Layer 3 external outside network.
Associates infraInfra, an external routed domain (l3extDomP), with a tenant Layer 3 external instance profile (l3extInstP).
Supports routing protocols such as BGP, OSPF, and EIGRP, including supported combinations.
Enables reuse of outside network configuration for multiple nodes and supports failover or load balancing.
Layer 3 Out reference information
Routed connectivity to external networks is enabled by associating a fabric access (infraInfra) external routed domain (l3extDomP) with a tenant Layer 3 external instance profile (l3extInstP) or external EPG for a Layer 3 external outside network (l3extOut).
The l3extOut object includes routing protocol options, such as BGP, OSPF, or EIGRP, and switch-specific and interface-specific configurations.
The l3extOut contains the routing protocol, such as OSPF with its related VRF and area ID.
The Layer 3 external interface profile contains the required OSPF interface details.
Both the l3extOut and the interface profile are required to enable OSPF.
The l3extInstP EPG exposes the external network to tenant EPGs through a contract.
A tenant EPG can communicate through a contract with the l3extInstP EPG according to the network configuration in the l3extOut.
Outside network configuration can be reused for multiple nodes by associating the nodes with the Layer 3 external node profile.
Multiple nodes using the same profile can be configured for failover or load balancing.
A node can be added to multiple l3extOut objects, causing the VRFs associated with those objects to be deployed on that node.
For scalability information, refer to the current Verified Scalability Guide for Cisco ACI.
Layer 3 Out example
A tenant EPG containing a group of web servers can communicate through a contract with the l3extInstP EPG according to the network configuration in the l3extOut. This configuration can be reused for multiple nodes to support failover or load balancing.
Figure 1. Policy model for Layer 3 external connections
