HP Cisco Nexus 5000 Cisco Nexus 5000 Series Switch CLI Software Configuration - Page 633

About Reordering SAN Port Channel Frames, About Enabling In-Order Delivery

Page 633 highlights

Configuring Fibre Channel Routing Services and Protocols About Reordering SAN Port Channel Frames • 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 network. 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 and all old frames are flushed. Frames that cannot be delivered in order through the old path within the network latency drop period are dropped. Related Topics • Configuring the Drop Latency Time, page 589 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. OL-16597-01 Cisco Nexus 5000 Series Switch CLI Software Configuration Guide 587

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• 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
network.
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
and all old frames are flushed.
Frames that cannot be delivered in order through the old path within the network latency drop period are
dropped.
Related Topics
Configuring the Drop Latency Time, page 589
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.
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
OL-16597-01
587
Configuring Fibre Channel Routing Services and Protocols
About Reordering SAN Port Channel Frames