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32-16
Cisco MDS 9000 Family Fabric Manager Configuration Guide
OL-17256-03, Cisco MDS NX-OS Release 4.x
Chapter 32 Configuring Fibre Channel Routing Services and Protocols
In-Order Delivery
Figure 32-13 Route Change Delivery
In Figure 32-13, 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 treated 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 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 Link Congestion Delivery
In Figure 32-14, 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.
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 using the old path are delivered before new frames are accepted.
Switch 1 Switch 2 Switch 3
Switch 4
Frame 2 Frame 1
Frame 4 Frame 3
Old path
New path
85474
Switch 1 Switch 2
Frame 2 Frame 1
Frame 4 Frame 3
Old path
New path
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