Connectrix: What is an In-order Delivery Guarantee

In-order delivery (IOD) Guarantee feature attempts to minimize the number of frames dropped during Port Channel link changes when the in-order delivery is enabled. It sends a request to the remote switch on the Port Channel to flush all frames for this Port Channel.

When the IOD guarantee feature is enabled and a Port Channel link change occurs, the frames crossing the Port Channel are treated as follows:

1. Frames using the old path are delivered before new frames are accepted.
2. The new frames are delivered through the new path after the switch latency drop period has elapsed and all old frames are flushed.

When should you use this Feature?
The recommendation is to enable this feature when devices that cannot handle any out-of-order frames are present in the switch.

Load-balancing algorithms within the Connectrix 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 is delayed because of an intentional pausing of fabric forwarding to purge the fabric of resident frames that may potentially be forwarded out-of-order.

Advantages:

• In-order delivery Guarantee enabled helps to stop receiving the out-of-order frames.
• In-order delivery of data frames guarantees frame delivery to a destination in the same order that were sent by the originator.

Disadvantages:

• Whenever IOD is enabled per switch, the switch holds the incoming traffic for 2 seconds/ frame (the default value). This means that the switch adds 2 seconds of latency.

Hence there would be a slight drop in the performance of the end device connected to the switches.