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Forwarding Class Queue Assignments
J-series Services Routers and SRX-series services gateways have
eight queues built into the hardware. By default, four queues are
assigned to four forwarding classes. Table 179 shows the four default
forwarding classes and queues that Juniper Networks classifiers assign
to packets based on the CoS values in arriving packet headers. Queues
4 through 7 have no default assignments to forwarding classes. To
use queues 4 through 7, you must create custom forwarding class names
and assign them to the queues. For more information about how to assign
queues to forwarding classes, see Configuring Class of Service.
By default, all incoming packets, except the IP protocol control
packets, are assigned to the forwarding class associated with queue
0. All IP protocol control packets are assigned to the forwarding
class associated with queue 3.
Table 179 displays the
default assignments of forwarding classes to queues.
Table 179: Default
Forwarding Class Queue Assignments
|
Forwarding Queue
|
Forwarding Class
|
Forwarding Class Description
|
|
Queue 0
|
best-effort (BE)
|
The Juniper Networks device does not apply any special CoS handling
to packets with 000000 in the DiffServ field, a backward compatibility
feature. These packets are usually dropped under congested network
conditions.
|
|
Queue 1
|
expedited-forwarding (EF)
|
The Juniper Networks device delivers assured bandwidth, low
loss, low delay, and low delay variation (jitter) end-to-end for packets
in this service class.
Devices accept excess traffic in this class, but in contrast
to assured forwarding, out-of-profile expedited-forwarding packets
can be forwarded out of sequence or dropped.
|
|
Queue 2
|
assured-forwarding (AF)
|
The Juniper Networks device offers a high level of assurance
that the packets are delivered as long as the packet flow from the
customer stays within a certain service profile that you define.
The device accepts excess traffic, but applies a random early
detection (RED) drop profile to determine whether the excess packets
are dropped and not forwarded.
Three drop probabilities (low, medium, and high) are defined
for this service class.
|
|
Queue 3
|
network-control (NC)
|
The Juniper Networks device delivers packets in this service
class with a low priority. (These packets are not delay sensitive.)
Typically, these packets represent routing protocol hello or
keepalive messages. Because loss of these packets jeopardizes proper
network operation, delay is preferable to discard.
|
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