Overview of CoS Upgrade Requirements to Junos OS Release 12.3
Before you upgrade to Junos OS Release 12.3, you might need to edit the class-of-service (CoS) configuration, because the way the QFX Series handles lossless forwarding classes has changed in Junos OS Release 12.3.
By default, the fcoe and no-loss forwarding classes are mapped to output queue 3 and output queue 4, respectively, and to IEEE 802.1p priority 3 (code point 011) and priority 4 (code point 100), respectively. These are the only two forwarding classes (and the only two queues) that support lossless transport in the default configuration.
If you use the default CoS configuration, you do not need to edit the CoS configuration after upgrading to Junos OS Release 12.3 because the default CoS configuration is backward compatible.
Junos OS Release 12.3 increases the support for lossless forwarding classes (priorities) from two forwarding classes to six forwarding classes. To support configuring lossless forwarding classes, Junos OS Release 12.3 introduces a new option to forwarding class configuration: the no-loss packet drop attribute.
 | Note: The new no-loss packet drop attribute and the previously existing no-loss default forwarding class have the same name, but they are not the same. You can use the no-loss packet drop attribute on any unicast forwarding class. |
If you explicitly configure any lossless forwarding class (including explicitly configuring the default fcoe and no-loss forwarding classes), you must specify the no-loss packet drop attribute to obtain lossless behavior. If you do not explicitly configure the fcoe and no-loss forwarding classes, those forwarding classes remain lossless.
The addition of the no-loss packet drop attribute to forwarding class configuration means that when you upgrade from an earlier release to Junos OS Release 12.3, the new software might not preserve the lossless forwarding class configuration of the fcoe and no-loss forwarding classes.
If you used the default forwarding class configuration for the fcoe and no-loss forwarding classes, the CoS configuration is backward compatible. You do not have to do anything to preserve the lossless behavior of traffic that uses those forwarding classes when you upgrade to Junos OS Release 12.3. (This is because the default configuration of these two forwarding classes includes the no-loss packet drop attribute.)
However, if you explicitly configured the fcoe or the no-loss forwarding class by including the set forwarding-classes class forwarding-class-name queue-num queue-number at the [edit class-of-service] hierarchy level, then those forwarding classes are no longer lossless, they are lossy. In Junos OS Release 12.3 and later, you must include the no-loss packet drop attribute in any explicit forwarding class configuration to configure a lossless forwarding class.
For example, before Junos OS Release 12.3, the following explicit configuration resulted in a lossless forwarding class:
user@switch# set class-of-service forwarding-classes
class fcoe queue-num 3However, in Junos OS Release 12.3, this configuration is lossy because it does not include the no-loss packet drop attribute. To preserve lossless behavior, after upgrading to Junos OS Release 12.3, you need to add the no-loss drop attribute:
user@switch# set class-of-service forwarding-classes
class fcoe queue-num 3 no-lossAlternatively, you can delete the explicit configuration before you upgrade to Junos OS Release 12.3 so that the system uses the default forwarding class, which is lossless:
user@switch# delete class-of-service forwarding-classes
class fcoe queue-num 3 | Note: The explicit configuration of other forwarding classes does not affect the lossless (or lossy) state of the fcoe and no-loss forwarding classes, because only the fcoe and no-loss forwarding classes are lossless forwarding classes before Junos OS Release 12.3. For example, if you explicitly configured the best-effort forwarding class but you used the default fcoe and no-loss forwarding classes in Junos OS Release 12.2, then when you upgrade to Junos OS Release 12.3, the fcoe and no-loss forwarding classes are still lossless (and the best-effort forwarding class retains its explicit configuration). |
| Note: To achieve lossless behavior for the traffic belonging to any forwarding class, you must also enable PFC on the IEEE 802.1p priority mapped to the forwarding class and ensure that DCBX exchanges the protocol TLVs for the application with the connected peer. |
