A virtual port channel (vPC) allows
links that are physically connected to two different Cisco Nexus 9000 Series
devices to appear as a single port channel by a third device (see figure). The
third device can be a switch, server, or any other networking device that
supports port channels. A vPC can provide Layer 2 multipathing, which allows
you to create redundancy and increase the bisectional bandwidth by enabling
multiple parallel paths between nodes and allowing load balancing traffic.
Figure 1. vPC Architecture
You can use only Layer 2 port channels in the vPC. A vPC domain is
associated to a single Virtual Device Context (VDC), so all vPC interfaces
belonging to a given vPC domain must be defined in the same VDC.
You configure the port channels by using one of the following:
When you configure the port channels in a vPC—including the vPC peer
link channel—without using LACP, each device can have up to eight active links
in a single port channel. When you configure the port channels in a
vPC—including the vPC peer link channels—using LACP, each device can have eight
active links and eight standby links in a single port channel. (See the “vPC
Interactions with Other Features” section for more information on using LACP
You must enable the vPC feature before you can configure or run the
The system automatically takes a checkpoint prior to disabling the
feature, and you can roll back to this checkpoint.
After you enable the vPC functionality, you create the peer-keepalive
link, which sends heartbeat messages between the two vPC peer devices.
You can create a vPC peer link by configuring a port channel on one
Cisco Nexus 9000 Series chassis by using two or more 10-Gigabit Ethernet ports
or 40-Gigabit Ethernet ports. To ensure that you have the correct hardware to
enable and run a vPC, enter the
show hardware feature-capability command. If
you see an X across from the vPC in your command output, your hardware cannot
enable the vPC feature.
We recommend that you configure the vPC peer link Layer 2 port channels
as trunks. On another Cisco Nexus 9000 Series chassis, you configure another
port channel again using two or more 10-Gigabit Ethernet ports or 40-Gigabit
Ethernet ports in the dedicated port mode. Connecting these two port channels
creates a vPC peer link in which the two linked Cisco Nexus devices appear as
one device to a third device. The third device, or downstream device, can be a
switch, server, or any other networking device that uses a regular port channel
to connect to the vPC. If you are not using the correct module, the system
displays an error message.
We recommend that you configure the vPC peer links on dedicated ports
of different modules to reduce the possibility of a failure. For the best
resiliency scenario, use at least two modules.
If you must configure all the vPC peer links and core-facing interfaces
on a single module, you should configure a track object that is associated with
the Layer 3 link to the core and on all the links on the vPC peer link on both
vPC peer devices. Once you configure this feature and if the primary vPC peer
device fails, the system automatically suspends all the vPC links on the
primary vPC peer device. This action forces all the vPC traffic to the
secondary vPC peer device until the system stabilizes.
You can create a track object and apply that object to all links on the
primary vPC peer device that connect to the core and to the vPC peer link. See
Cisco Nexus 9000 Series NX-OS Unicast Routing Configuration
Guide for information about the
track interface command.
The vPC domain includes both vPC peer devices, the vPC peer-keepalive
link, the vPC peer link, and all of the port channels in the vPC domain
connected to the downstream device. You can have only one vPC domain ID on each
In this version, you can connect each downstream device to a single vPC
domain ID using a single port channel.
Always attach all vPC devices using port channels to both vPC peer
A vPC (see figure) provides the following benefits:
Figure 2. vPC Interfaces in One VDC
Allows a single device to use a port channel across two upstream
Eliminates Spanning Tree Protocol (STP) blocked ports
Provides a loop-free topology
Uses all available uplink bandwidth
Provides fast convergence if either the link or a device fails
Provides link-level resiliency
Assures high availability