Cisco Cisco Nexus 5010 Switch Guida Alla Progettazione
Design Guide
Figure 7.
LACP Behavior with Various Wiring Configurations
System ID in a vPC System
Spanning tree and LACP use the switch MAC address for bridge ID field in the spanning tree bridge protocol data unit
(BPDU) and as part of LACP LAGID, respectively. In a single chassis, they use the systemwide MAC address for this
purpose. For systems that use vPCs, using the systemwide MAC address would not work because the vPC peers
needs to appear as a single entity as exemplified in Figure 7-C. In order to address this requirement, vPC offers
either an automatic configuration or a manual configuration of the system-id for the vPC peers.
(BPDU) and as part of LACP LAGID, respectively. In a single chassis, they use the systemwide MAC address for this
purpose. For systems that use vPCs, using the systemwide MAC address would not work because the vPC peers
needs to appear as a single entity as exemplified in Figure 7-C. In order to address this requirement, vPC offers
either an automatic configuration or a manual configuration of the system-id for the vPC peers.
The automatic solution implemented by vPC consists in generating a system ID composed of a priority and MAC
address, where the MAC is derived from a reserved pool of MAC addresses combined with the domain ID specified in
the vPC configuration. The domain ID is encoded in the last octet and the trailing 2 bits of the previous octet of the
MAC address.
address, where the MAC is derived from a reserved pool of MAC addresses combined with the domain ID specified in
the vPC configuration. The domain ID is encoded in the last octet and the trailing 2 bits of the previous octet of the
MAC address.
By configuring domain IDs to be different on adjacent vPC complexes (and to be identical on each vPC peer
complex), you will ensure the uniqueness of the system ID for LACP negotiation purposes. You also guarantee that
the Spanning Tree Protocol BPDUs use a MAC address that is representative of the vPC complex.
complex), you will ensure the uniqueness of the system ID for LACP negotiation purposes. You also guarantee that
the Spanning Tree Protocol BPDUs use a MAC address that is representative of the vPC complex.
It is also possible to override the automatic generation of the system ID by using the CLI and configuring the system-
id on both vPC peers, as follows:
id on both vPC peers, as follows:
(config-vpc-domain)#system-mac <mac>
Primary and Secondary vPC Roles
In a vPC system, one vPC switch is defined as primary and one is defined as secondary, based on defined priorities.
The lower number has higher priority, so it wins.
The lower number has higher priority, so it wins.
Also, these roles are nonpreemptive, so a device may be operationally primary, but secondary from a configuration
perspective.
perspective.
© 2010 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information.
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