HP Cisco MDS 9020 Cisco MDS 9000 Family Fabric Manager Configuration Guide - R - Page 728

In-Order Delivery Chapter 32 Configuring Fibre Channel Routing Services and Protocols Send documentation comments to [email protected] Figure 32-13 Route Change Delivery Switch 1 Switch 2 Switch 3 Frame 2 Frame 1 Old path New path 85474 Frame 4 Frame 3 Switch 4 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 Switch 1 Frame 2 Frame 1 Switch 2 Old path New path Frame 4 Frame 3 85475 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. 32-16 Cisco MDS 9000 Family Fabric Manager Configuration Guide OL-17256-03, Cisco MDS NX-OS Release 4.x