Vpc Peer Link Overview - Cisco Nexus 3548 Configuration Manual

vPC Peer Link Overview

vPC Peer Link Overview
You can have only two switches as vPC peers; each switch can serve as a vPC peer to only one other vPC
peer. The vPC peer switches can also have non-vPC links to other switches.
To make a valid configuration, you configure an EtherChannel on each switch and then configure the vPC
domain. You assign the EtherChannel on each switch as a peer link. For redundancy, we recommend that you
should configure at least two dedicated ports into the EtherChannel; if one of the interfaces in the vPC peer
link fails, the switch automatically falls back to use another interface in the peer link.
Note We recommend that you configure the EtherChannels in trunk mode.
Many operational parameters and configuration parameters must be the same in each switch connected by a
vPC peer link. Because each switch is completely independent on the management plane, you must ensure
that the switches are compatible on the critical parameters. vPC peer switches have separate control planes.
After configuring the vPC peer link, you should display the configuration on each vPC peer switch to ensure
that the configurations are compatible.
Note
You must ensure that the two switches connected by the vPC peer link have certain identical operational and
configuration parameters.
When you configure the vPC peer link, the vPC peer switches negotiate that one of the connected switches
is the primary switch and the other connected switch is the secondary switch. By default, the Cisco NX-OS
software uses the lowest MAC address to elect the primary switch. The software takes different actions on
each switch—that is, the primary and secondary—only in certain failover conditions. If the primary switch
fails, the secondary switch becomes the operational primary switch when the system recovers, and the previously
primary switch is now the secondary switch.
You can also configure which of the vPC switches is the primary switch. If you want to configure the role
priority again to make one vPC switch the primary switch, configure the role priority on both the primary and
secondary vPC switches with the appropriate values, shut down the EtherChannel that is the vPC peer link
on both switches by entering the shutdown command, and reenable the EtherChannel on both switches by
entering the no shutdown command.
MAC addresses that are learned over vPC links are also synchronized between the peers.
Configuration information flows across the vPC peer links using the Cisco Fabric Services over Ethernet
(CFSoE) protocol. All MAC addresses for those VLANs configured on both switches are synchronized
between vPC peer switches. The software uses CFSoE for this synchronization.
If the vPC peer link fails, the software checks the status of the remote vPC peer switch using the peer-keepalive
link, which is a link between vPC peer switches, to ensure that both switches are up. If the vPC peer switch
is up, the secondary vPC switch disables all vPC ports on its switch. The data then forwards down the remaining
active links of the EtherChannel.
The software learns of a vPC peer switch failure when the keepalive messages are not returned over the
peer-keepalive link.
Use a separate link (vPC peer-keepalive link) to send configurable keepalive messages between the vPC peer
switches. The keepalive messages on the vPC peer-keepalive link determines whether a failure is on the vPC
Cisco Nexus 3548 Switch NX-OS Interfaces Configuration Guide, Release 9x
64
Configuring Virtual Port Channels