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

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Ethernet queues used for hashed load balancing are always present in the scheduler
hierarchy.
To ensure that QoS is symmetrically applied to all the links, the router periodically
rebalances the load within the LAG using a hash algorithm. You can control the
loadbalancing parameters and configure the system to dynamically rebalance.
Partitioning the Scheduler Hierarchy
The system then partitions the scheduler hierarchy by binding the IP, VLAN,
L2TP session, and MPLS resources for each subscriber to a selected link within the
LAG at the time the subscriber interface is configured.
S-VLANs and Subscriber Load Balancing
The system clones S-VLAN nodes and queues on each link in the LAG. The system
clone S-VLANs so it can allocate subscribers that share a common S-VLAN ID to
different links within the LAG. S-VLAN nodes and queues are the only resources that
are cloned; the system always allocates nodes and queues for other interface types
to a single selected link.
Cloning S-VLAN nodes enables fine-grained load balancing within the LAG because
VLANs within the S-VLAN can be allocated to the link with the least traffic. However,
cloned S-VLANs can introduce anomalous scheduling behavior. A shaped S-VLAN
node within the LAG shapes traffic on a per-link basis. Shaping a LAG S-VLAN node
to 2 Mbps on a LAG with 2 links can enable up to 4 Mbps of traffic (2 Mbps per link).
Shared shaping on an S-VLAN within a LAG has the same behavior; the LAG S-VLAN
that is shared shaped to 10 Mbps on a LAG with 2 ports allows up to 20Mbps of
traffic; 10 Mbps for each link.
PPPoE over VLANs and Subscriber Load Balancing
The system binds PPPoE subscribers stacked over a common VLAN to the same link
within the LAG. Because the underlying VLAN node is allocated to a single link, the
system allocates all traffic over that VLAN to that link.
PPPoE over Ethernet (No VLANs) and Subscriber Load Balancing
The system allocates subscribers to each link independently. There are no S-VLAN
nodes to clone, and no related VLAN nodes that require allocation on the same link.
MPLS over LAG and Subscriber Load Balancing
For QoS purposes, the system considers base tunnels as logical interfaces, but does
not consider stacked tunnels. The system assigns MPLS base tunnels stacked over
VLANs to the link to which the VLAN is assigned.
Subscriber Load Balancing for 802.3ad Link Aggregation Groups Overview
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Chapter 21: Configuring QoS for 802.3ad Link Aggregation Groups