HP Cisco Nexus 5000 Cisco Nexus 5000 Series Switch CLI Software Configuration - Page 178

Manually Con d vPC Features, shutdown

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Manually Configured vPC Features Information About vPCs 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. For known unicast traffic, you should use the local links of the vPC because you cannot load balance traffic across the peer link. Unknown unicast, multicast, and broadcast traffic are flooded across the vPC peer link. The software keeps the multicast forwarding state synchronized between the two peers for groups learned over the vPC link. If the multicast forwarding states are learned over isolated ports on either peer, the states are not synchronized, but since the peer link is a router port, the traffic is forwarded to the peer; the peer then handles the forwarding if there are other isolated ports on that switch. 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 to prevent loops and disappearing or flooding traffic. 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 peer link only or on the vPC peer switch. The keepalive messages are used only when all the links in the peer link fail. Manually Configured vPC Features You must manually configure the following features to conform to the primary/secondary mapping of each of the vPC peer devices: • STP root-Configure the primary vPC peer device as the highest STP root priority, and configure the secondary device with a lower root priority. We recommend that you configure the vPC peer link interfaces as STP network ports so that Bridge Assurance is enabled on all vPC peer links We recommend that you configure Rapid PVST+ so that the primary device is the root for all VLANs and configure MST so that the primary device is the root for all instances. Cisco Nexus 5000 Series Switch CLI Software Configuration Guide 132 OL-16597-01

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You must ensure that the two switches connected by the vPC peer link have certain identical operational
and configuration parameters.
Note
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.
For known unicast traffic, you should use the local links of the vPC because you cannot load balance traffic
across the peer link. Unknown unicast, multicast, and broadcast traffic are flooded across the vPC peer link.
The software keeps the multicast forwarding state synchronized between the two peers for groups learned
over the vPC link. If the multicast forwarding states are learned over isolated ports on either peer, the states
are not synchronized, but since the peer link is a router port, the traffic is forwarded to the peer; the peer then
handles the forwarding if there are other isolated ports on that switch.
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 to prevent loops and disappearing or
flooding traffic. 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
peer link only or on the vPC peer switch. The keepalive messages are used only when all the links in the peer
link fail.
Manually Configured vPC Features
You must manually configure the following features to conform to the primary/secondary mapping of each
of the vPC peer devices:
• STP root—Configure the primary vPC peer device as the highest STP root priority, and configure the
secondary device with a lower root priority.
We recommend that you configure the vPC peer link interfaces as STP network ports so that Bridge
Assurance is enabled on all vPC peer links
We recommend that you configure Rapid PVST+ so that the primary device is the root for all VLANs
and configure MST so that the primary device is the root for all instances.
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
132
OL-16597-01
Information About vPCs
Manually Configured vPC Features