Cisco Systems N5KC5596TFA manual Guidelines and Limitations for vPCs, vPC Peer Switch

Configuring Virtual Port Channels

vPC Peer Switch

Note Do not enter the no cfs eth distribute or the no cfs distribute command. CFSoE must be enabled for vPC functionality. If you do enter either of these commands when vPC is enabled, the system displays an error message.

When you enter the show cfs application command, the output displays "Physical-eth," which shows the applications that are using CFSoE.

vPC Peer Switch

The vPC peer switch feature addresses performance concerns around STP convergence. This feature allows a pair of Cisco Nexus devices to appear as a single STP root in the Layer 2 topology. This feature eliminates the need to pin the STP root to the vPC primary switch and improves vPC convergence if the vPC primary switch fails.

To avoid loops, the vPC peer link is excluded from the STP computation. In vPC peer switch mode, STP BPDUs are sent from both vPC peer devices to avoid issues related to STP BPDU timeout on the downstream switches, which can cause traffic disruption.

This feature can be used with the pure peer switch topology in which the devices all belong to the vPC.

Note Peer-switch feature is supported on networks that use vPC and STP-based redundancy is not supported. If the vPC peer-link fail in a hybrid peer-switch configuration, you can lose traffic. In this scenario, the vPC peers use the same STP root ID as well same bridge ID. The access switch traffic is split in two with half going to the first vPC peer and the other half to the second vPC peer. With the peer link failed, there is no impact on north/south traffic but east-west traffic will be lost (black-holed).

For information on STP enhancement features and Rapid PVST+, see the Layer 2 Switching Configuration Guide for your device.

Guidelines and Limitations for vPCs

vPC has the following configuration guidelines and limitations:

•You must enable the vPC feature before you can configure vPC peer-link and vPC interfaces.

•You must configure the peer-keepalive link before the system can form the vPC peer link.

•The vPC peer-link needs to be formed using a minimum of two 10-Gigabit Ethernet interfaces.

•You can connect a pair of Cisco Nexus 5000 Series switches or a pair of Cisco Nexus 5500 Series switches in a vPC directly to another switch or to a server. vPC peer switches must be of the same type, for example, you can connect a pair of Nexus 5000 series switches or a pair of Nexus 5500 Series switches but you cannot connect a Nexus 5000 Series switch to a Nexus 5500 Series switch in a vPC topology.

•Only port channels can be in vPCs. A vPC can be configured on a normal port channel (switch-to-switch vPC topology), on a port channel fabric interface (fabric extender vPC topology), and on a port channel host interface (host interface vPC topology).

Cisco Nexus 5000 Series NX-OS Interfaces Configuration Guide, Release 5.2(1)N1(1)

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