About Reordering San Port Channel Frames; About Enabling In-Order Delivery - Cisco Nexus 5000 Series Configuration Manual

Configuring Fibre Channel Routing Services and Protocols
In the figure above, the new path from Switch 1 to Switch 4 is faster. In this scenario, Frame 3 and Frame 4
may be delivered before Frame 1 and Frame 2.
If the in-order guarantee feature is enabled, the frames within the network are delivered as follows:
• 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 30: 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, on page 157

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.
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 in the 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
OL-xxxxx-xx
Cisco Nexus 5000 Series NX-OS SAN Switching Configuration Guide
In-Order Delivery
155