Cisco Nexus – Enabling Layer 3 Routing on vPC Peer Links with “layer3 peer-router”

The world of networking is in constant evolution. Among the players steering this transformation are Cisco Nexus switches, renowned for their prowess in data center settings. One standout feature they offer is the Virtual Port Channel (vPC), designed for high availability and redundancy. However, the conventional vPC primarily catered to Layer 2 functionalities. The layer3 peer-router command enters the stage to infuse Layer 3 routing capabilities over the vPC peer link.

vPC in a Nutshell

A vPC allows links physically connected to two Nexus switches to appear to a third device as a single port channel. By its default nature, the vPC peer link — the backbone of this configuration — operates exclusively at Layer 2. It offers redundancy and negates loop scenarios without blocking any ports but poses challenges when Layer 3 routing comes into play. A significant hurdle was the inability of one vPC peer to utilize the vPC peer link for routing if its upstream connectivity was compromised, even when the other peer remained fully functional.

The Emergence of layer3 peer-router

This command breaks through the Layer 3 barrier on vPC. Here’s how it operates:

1. Routing Adjacency Over vPC Peer Link: The layer3 peer-router command allows BGP to form peerings and exchange routes over the vPC peer link.

2. Enhanced Resiliency: In scenarios where one vPC peer loses its primary network connectivity, it isn’t left stranded. Through layer3 peer-router, it can now glean vital routing information from its peer, guaranteeing continuity in Layer 3 operations.

3. Optimized Traffic Flow: While the command’s chief objective is maintaining routing continuity and not necessarily forwarding transit traffic over the link, it indirectly fosters improved traffic distribution.

4. Support for Advanced Features: The command heralds support for functionalities like IP multicast routing within the vPC setup.

The BGP Edge in vPC Context

Border Gateway Protocol (BGP) is paramount in inter-network communications. Here’s why using BGP in this context is pivotal:

  • Granular Routing Control: BGP offers unmatched control over routing decisions, which can be invaluable in a vPC setup.
  • Stable Peering with Router Neighbors: BGP’s stability ensures that even in dynamic environments, routing adjacencies remain consistent. When a Nexus switch is peering with a router neighbor via BGP over the vPC setup, this stability ensures that both Nexus switches are aware of routes and can handle traffic forwarding, even if one of them faces a disruption.
  • Route Path Diversity: BGP allows multiple paths for the same prefix, providing path diversity and redundancy — crucial in a vPC environment for load sharing and failover.

Benefits of Layer 3 Routing on vPC Peer Link with BGP

Incorporating BGP into the layer3 peer-router configuration on Cisco Nexus switches ushers in numerous advantages:

  • Swift Convergence: React promptly to route changes or peer outages.
  • Efficient Traffic Management: Harness all available links for optimal bandwidth utilization.
  • Bypass Bottlenecks: Distribute traffic across both vPC peers, mitigating potential network congestion points.
  • Augmented Routing Potential: The blend of high availability with BGP’s rich feature set enriches the vPC configuration.


Cisco Nexus switches, armed with the layer3 peer-router command, stand poised to bridge the gap between Layer 2 and Layer 3 domains in vPC setups, all while harnessing the power of BGP. It affirms networking’s progressive nature, ensuring modern enterprises stay robustly connected.

Strong Recommendation

    • Activate peer-gateway prior to enabling the layer3 peer-router.
  • For effective implementation, ensure layer3 peer-router is configured on both vPC peers.