Juniper QFX3000-G QFabric, Deployment Manual, Page: 92 / 652

Table 9: Default Forwarding Class to Fabric Forwarding Class Set
Mapping
(continued)
Maximum
MTU
Supported
for Lossless
Operation
Fabric
Output
Queue
Fabric Forwarding Class
Set
Forwarding Class
9k 5 fabric_fcset_noloss5 No forwarding classes are mapped by
default to this hidden fabric fc-set.
9k 6 fabric_fcset_noloss6 No forwarding classes are mapped by
default to this hidden fabric fc-set.
NA 9 fabric_fcset_multicast2 No forwarding classes are mapped by
default to this hidden fabric fc-set.
NA 10 fabric_fcset_multicast3 No forwarding classes are mapped by
default to this hidden fabric fc-set.
NA 11 fabric_fcset_multicast4 No forwarding classes are mapped by
default to this hidden fabric fc-set.
The maximum fiber cable length between the QFabric system Node device and the
QFabric system Interconnect device is 150 meters.
TIP: If you explicitly configure lossless forwarding classes, we recommend
that you map each user-configured lossless forwarding class to an unused
fabric fc-set (fabric_fcset_noloss3 through fabric_fcset_noloss6) on a
one-to-one basis: one lossless forwarding class mapped to one lossless
fabric fc-set.
The reason for one-to-one mapping is to avoid fate sharing of lossless flows.
Because each fabric fc-set is mapped statically to an output queue, when
you map more than one forwarding class to a fabric fc-set, all of the traffic
in all of the forwarding classes that belong to the fabric fc-set uses the same
output queue. If that output queue becomes congested due to congestion
caused by one of the flows, the other flows are also affected. (They share
fate because the flow that congests the output queue affects flows that are
not experiencing congestion.)
However, it is important to understand that fabric_fcset_noloss1 and
fabric_fcset_noloss2 have a scheduling weight of 35, while the other fabric
fc-sets have a scheduling weight of 1. The scheduling weights mean that
fabric_fcset_noloss1 and fabric_fcset_noloss2 receive most of the bandwidth
available to lossless fabric fc-sets if the amount of traffic on
fabric_fcset_noloss1 and fabric_fcset_noloss2 requires the bandwidth.
If you believe that the traffic on fabric_fcset_noloss1 and fabric_fcset_noloss2
will consume most of that bandwidth, then you should place all lossless
Copyright © 2015, Juniper Networks, Inc. 66
QFX3000-G QFabric System Deployment Guide