About Reordering Portchannel Frames; About Enabling In-Order Delivery - HP Cisco MDS 9216 - Fabric Switch Configuration Manual

Chapter 32 Configuring Fibre Channel Routing Services and Protocols
S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m

About Reordering PortChannel Frames

When a link change occurs in a PortChannel, the frames for the same exchange or the same flow can
switch from one path to another faster path.
Figure 32-14
Switch 1
In Figure
can be delivered before Frame 1 and Frame 2.
The the in-order delivery feature attempts to minimize the number of frames dropped during
PortChannel link changes when the in-order delivery is enabled by sending a request to the remote switch
on the PortChannel to flush all frames for this PortChannel.
Note Both switches on the PortChannel must be running Cisco SAN-OS Release 3.0(1) for this IOD
enhancement. For earlier releases, IOD waits for the switch latency period before sending new frames.
When the in-order delivery guarantee feature is enabled and a PortChannel link change occurs, the
frames crossing the PortChannel are treated as follows:
•
•
Frames that cannot be delivered in order through the old path within the switch latency drop period are
dropped. See the

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 MDS 9000 Family.
Tip 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 MDS 9000 Family 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 this 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-16184-01, Cisco MDS SAN-OS Release 3.x
Link Congestion Delivery
Frame 2
Frame 4
32-14, the port of the old path (red dot) is congested. In this scenario, Frame 3 and Frame 4
Frames using the old path are delivered before new frames are accepted.
The new frames are delivered through the new path after the switch latency drop period has elapsed
and all old frames are flushed.
"Configuring the Drop Latency Time" section on page
Switch 2
Frame 1
Frame 3
Cisco MDS 9000 Family CLI Configuration Guide
In-Order Delivery
Old path
New path
32-18.
32-17