Руководство По Проектированию для Cisco Cisco Nexus 5010 Switch
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To reduce the traffic loss for single-attached devices (which may be attached to the vPC primary device), you may
want to tune the peer keepalive timer as follows:
nexus5500-1(config-vpc-domain)# peer-keepalive destination <destination IP>
interval <ms>
interval <ms>
Split-Brain Scenarios
When two vPC peers become completely disconnected, they cannot synchronize either unicast or multicast MAC
address entries. This lack of synchronization can cause flooding for unicast traffic and traffic drops for multicast
traffic.
To reduce traffic loss when two vPC peers are disconnected, the peer keepalive connection is used by the vPC
peers. If the peer link is missing and the peer keepalive connectivity is still present, the vPC primary switch keeps
the vPCs active, while the vPC secondary switch shuts down the vPC member ports. This approach helps ensure
uninterrupted traffic connectivity across the vPC primary switch path.
If both the vPC peer link and peer keepalive become disconnected, all vPCs are kept active because this failure is
undistinguishable from the loss of a vPC peer.
This scenario works fine in double-sided vPC topologies, but it can introduce loops in designs like the one shown in
Figure 2.In addition, spanning-tree disputes can occur in this particular design when both the peer link and the peer
keepalive are absent.
Split-Brain Scenarios After a Reload Operation
A particular case of a split-brain scenario occurs when the peer keepalive connectivity disappears, and afterwards
the vPC peers are reloaded.
Initially when peer keepalive connectivity disappears, vPC keeps functioning, because the keepalive is not strictly
necessary for the correct forwarding of frames in a vPC topology.
If the vPCs peers then subsequently reload, when they become active, the lack of peer keepalive connectivity
prevents the vPC domain from forming. This scenario would keep the vPC ports down, unless autorecovery is
configured.
In this particular case, if autorecovery is configured, the vPC peers bring up their vPC ports, without bringing up the
vPC peer link. The result is a split-brain scenario, which can cause loops and spanning-tree disputes as described
in the previous section.
Cisco Nexus 5000 Series vPC Advanced Considerations
Configuration Consistency for PortChannels
The Ethernet PortChannel capability allows links to be bundled to form a single entity if certain compatibility
conditions are met. The following is a list of conditions that are verified before ports can form a regular PortChannel
(this list refers to regular PortChannels, not vPCs). Members must:
●
Have the same port mode configured
●
Have the same speed configured; if they are configured with speed set to automatic, they have to negotiate
the same speed when they become active, and if a member negotiates a different speed, it will be
suspended
●
Have the same MTU value configured