Juniper JUNOSE 11.1.X - QUALITY OF SERVICE CONFIGURATION GUIDE 3-21-2010, Configuration Manual

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In an ideal QoS configuration, queues and nodes are stacked over a single port that
corresponds to a LAG, with the port bandwidth equal to the sum of the overall port
bandwidth.
However, the actual LAG behavior is different. No level 1 node or queue can exceed
the bandwidth of a link. The relative weighting of queues and nodes results in
proportional bandwidth allocation only within a link, but not across the entire LAG.
Actual traffic might not be evenly balanced across links in the LAG, resulting in latency
and loss on one link, while another link may be lightly loaded.
Even though relative weighting is different on a LAG, shaping and shared shaping in
the partitioned scheduler hierarchy operate in the same way as a typical Ethernet
configuration.
Related Topics
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For more information about load rebalancing, see Configuring Load Rebalancing
for 802.3ad Link Aggregation Groups on page 193
Guidelines for Configuring QoS over 802.3ad Link Aggregation Groups
When you configure QoS over 802.3ad LAGs, be sure to consider the following
behaviors:
■
QoS profiles cannot be attached to Ethernet ports if the port is a member of a
LAG. In typical QoS configurations, the Ethernet interface is considered the root
of the interface hierarchy. When you configure QoS for 802.3ad link aggregation,
the LAG interface is considered the root of the interface hierarchy.
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You cannot configure hierarchical QoS for IP configured directly over a LAG
interface.
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You cannot obtain QoS information or statistics for IP interfaces stacked over a
LAG interface using any of the
show commands for QoS. Instead, the show qos
scheduler-hierarchy command is designed to find the interface hierarchy rooted
at the specified interface and report all scheduler nodes and queues managed
by those interfaces. The typical defaults in QoS profiles such as ethernet-default
and atm-default specify the "ip queue traffic-class best-effort" rule, so those
queues are reported in the interface hierarchy. The lag-default QoS profile does
not specify this rule by default.
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Do not attach QoS profiles to IP or VLAN subinterfaces in a LAG that contain
downreferences (that is, rules for S-VLAN or Ethernet nodes or queues). QoS
profiles attached at subinterfaces above a LAG that also include downreference
create an asymmetric scheduler hierarchy. For example, one Ethernet port might
be shaped and not another.
Also, if the QoS profile specifies only Ethernet, then the traffic sent to the
subinterface might be only partially affected by the QoS profile, or not at all. The
traffic can be allocated to another port entirely.
Related Topics
Subscriber Load Balancing for 802.3ad Link Aggregation Groups Overview on
page 186
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190 ■
Guidelines for Configuring QoS over 802.3ad Link Aggregation Groups
JUNOSe 11.1.x Quality of Service Configuration Guide