In-Order Delivery; About Reordering Network Frames - HP Cisco MDS 9020 - Fabric Switch Configuration Manual

Chapter 25 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

In-Order Delivery

In-Order Delivery (IOD) of data frames guarantees frame delivery to a destination in the same order that
they were sent by the originator.
Some Fibre Channel protocols or applications cannot handle out-of-order frame delivery. In these cases,
switches in the Cisco MDS 9000 Family preserve frame ordering in the frame flow. The source ID (SID),
destination ID (DID), and optionally the originator exchange ID (OX ID) identify the flow of the frame.
On any given switch with IOD enabled, all frames received by a specific ingress port and destined to a
certain egress port are always delivered in the same order in which they were received.
Use IOD only if your environment cannot support out-of-order frame delivery.
If you enable the in-order delivery feature, the graceful shutdown feature is not implemented.
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About Reordering Network Frames

When you experience a route change in the network, the new selected path may be faster or less
congested than the old route.
Figure 25-5
Switch 1
In Figure
may be delivered before Frame 1 and Frame 2.
If the in-order guarantee feature is enabled, the frames within the network are treated as follows:
OL-16184-01, Cisco MDS SAN-OS Release 3.x
About Reordering Network Frames, page 25-13
About Reordering PortChannel Frames, page 25-15
About Enabling In-Order Delivery, page 25-15
Enabling In-Order Delivery Globally, page 25-16
Enabling In-Order Delivery for a VSAN, page 25-16
Displaying the In-Order Delivery Status, page 25-16
Configuring the Drop Latency Time, page 25-17
Displaying Latency Information, page 25-17
Route Change Delivery
Switch 2
Frame 2
25-5, the new path from Switch 1 to Switch 4 is faster. In this scenario, Frame 3 and Frame 4
Switch 3
Frame 1
Frame 4 Frame 3
Switch 4
Cisco MDS 9000 Family CLI Configuration Guide
In-Order Delivery
Old path
New path
25-13