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Port Channels and vPCs

Chapter Description

Port Channel technology allows multiple links between two participating devices to be used to forward traffic by using a load-balancing algorithm. vPC (virtual port channel) technology allows multiple devices to form a port channel. In this sample chapter from Cisco Data Center Fundamentals, the authors discuss Ethernet port channels, including port channel modes, port channel compatibility requirements, and port channel load balancing.

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Summary

This chapter discusses Ethernet port channels, virtual port channels (vPCs), and vPC configuration and verification, including the following points:

  • A port channel bundles physical links into a channel group to create a single logical link that provides an aggregate bandwidth of up to 32 physical links.

  • You can configure Layer 2 port channels in either access or trunk mode. Layer 3 port channel interfaces have routed ports as channel members. You cannot combine Layer 2 and Layer 3 interfaces in the same port channel.

  • Individual interfaces in port channels are configured with channel modes. When you run static port channels with no aggregation protocol, the channel mode is always set to on. When you configure LACP port channels, the channel mode is set to either active or passive.

  • In active mode, ports initiate negotiations with other ports by sending LACP packets. In passive mode, ports respond to LACP packets they receive but do not initiate LACP negotiation.

  • When you add an interface to a channel group, the NX-OS software checks certain interface and operational attributes to ensure that the interface is compatible with the channel group. If you configure a member port with an incompatible attribute, the software suspends that port in the port channel.

  • The Cisco NX-OS software load-balances traffic across all operational interfaces in a port channel by hashing the addresses in the frame to a numerical value that selects one of the links in the channel.

  • A vPC allows links that are physically connected to two different Cisco Nexus 7000 or 9000 Series devices to appear as a single port channel by a third device. You can use only Layer 2 port channels in the vPC.

  • vPC supports various topology implementations, including dual-uplink Layer 2 access, server dual-homing, and FEX dual-homed (active-active) vPC designs.

  • A vPC uses CFSoE as the primary control plane protocol for vPC.

  • vPC forwarding rule: a frame that enters the vPC peer switch from the peer-link cannot exit the switch from a vPC member port.

  • vPC interacts differently with events triggered by failure of vPC peer-keepalive link, vPC peer-link, and so on.

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