About Reordering San Port Channel Frames; About Enabling In-Order Delivery - Cisco AP775A - Nexus Converged Network Switch 5010 Configuration Manual

Configuring Fibre Channel Routing Services and Protocols
• Frames in the network are delivered in the order in which they are transmitted.
• Frames that cannot be delivered in order within the network latency drop period are dropped inside the

About Reordering SAN Port Channel Frames

When a link change occurs in a SAN port channel, the frames for the same exchange or the same flow can
switch from one path to another faster path.
Figure 73: Link Congestion Delivery
In the figure above, the port of the old path (red dot) is congested. In this scenario, Frame 3 and Frame 4 can
be delivered before Frame 1 and Frame 2.
When the in-order delivery feature is enabled and a port channel link change occurs, the frames crossing the
SAN port channel are delivered as follows:
• Frames using the old path are delivered before new frames are accepted.
• The new frames are delivered through the new path after the network latency drop period has elapsed
Frames that cannot be delivered in order through the old path within the network latency drop period are
dropped.
Related Topics
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About Enabling In-Order Delivery

You can enable the in-order delivery feature for a specific VSAN or for the entire switch. By default, in-order
delivery is disabled on switches in the Cisco Nexus 5000 Series.
We recommend that you only enable this feature when devices that cannot handle any out-of-order frames
are present in the switch. Load-balancing algorithms within the Cisco Nexus 5000 Series switch ensure that
frames are delivered in order during normal fabric operation. The load-balancing algorithms based on source
FC ID, destination FC ID, and exchange ID are enforced in hardware without any performance degradation.
However, if the fabric encounters a failure and the in-order delivery feature is enabled, the recovery will be
delayed because of an intentional pausing of fabric forwarding to purge the fabric of resident frames that could
potentially be forwarded out-of-order.
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network.
and all old frames are flushed.
Configuring the Drop Latency Time, page 589
About Reordering SAN Port Channel Frames
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
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