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Best Practices for Designing a Resilient and Scalable vPC Domain

August 15, 2021 ,

Best Practices for Designing a Resilient and Scalable vPC Domain

Virtual Port Channel (vPC) domains have evolved as an effective technique for enabling redundancy, scalability, and seamless communication. A vPC domain enables devices to connect to two distinct switches while appearing to the rest of the network as a single logical device. 

However, like with any network architecture, there are particular criteria and constraints that must be followed in order to successfully design and execute a vPC domain. In this post, we will look at the essential factors that influence the design of a strong vPC domain.


Cisco Datacenter Setup with vPC
Fig 1.1- Cisco Datacenter Setup with vPC

What is vPC Domain?

A pair of Cisco Nexus switches grouped together to function as a single logical switch for the devices connected to them is known as a vPC domain. You may utilize all available bandwidth and prevent STP-blocked ports by using a vPC domain. You must set up a vPC peer link between the two switches and give vPC IDs to the port channels that connect to the devices in order to build a vPC domain.

Guidelines and Restrictions

  • Before setting up a vPC domain, you must enable feature vPC (conf t; feature vpc).
  • For the vPC system to start up, you must configure peer-keepalive link before peer-link.
  • The configuration is not transferred from one device to the other; you must setup both vPC peer devices.
  • You must give each individual vPC layer a distinct vPC domain ID in order to establish a double-sided vPC topology.
  • You must give each every data center a distinct vPC domain ID if you want to utilize vPC in a DCI structure.
  • Verify that the required configuration settings are same on both side of the vPC peer-link.
  • We advise that you enable the LACP functionality and set the LACP mode to ACTIVE when configuring vPC member ports.
  • A particular vPC peer's ports must all be in the same VDC.
  • On vPC member ports, only Layer 2 port channels (switchport mode trunk or switchport mode access) may be specified.
  • PIM SM (Sparse Mode) and vPC are completely compatible. PIM BiDIR and PIM SSM (Source Specific Multicast) with vPC are not supported.
  • With vPC, DHCP relay and snooping are supported.
  • On vPC member ports, port security is not supported.
  • Instead of using the vPC peer-link and SVI for this purpose, configure a separate Layer 3 connection for routing from the vPC peer device (backup routing path).
  • To carry non-vPC VLAN traffic, install a second Layer 2 trunk port-channel as an interswitch link.
  • Use of default timers for HSRP (Hot Standby Router Protocol), VRRP (Virtual Router Redundancy Protocol), and PIM (Protocol Independent Multicast) settings while utilizing vPC is recommended.