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

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For subscriber load balancing, you configure the scheduler hierarchy with IP, VLAN,
and S-VLAN queues and the system allocates them to individual ports in the LAG.
The system demultiplexes each packet to an active link based on the subinterface
underlying the egress interface. For example, when an IP packet is routed to an IP
interface over a LAG, the system binds the underlying VLAN, PPPoE, or MPLS
subinterface to one of the active links in the LAG. The packet is transmitted over the
interface.
Most network operators configure QoS over 802.3ad LAGs using subscriber load
balancing to take advantage of subscriber class-based queueing (SCBQ) features.
However, configuring hashed load balancing is useful for achieving fine-grained
distribution of multicast VLAN traffic or for any high bandwidth VLAN that does not
require shared shaping.
To ensure that QoS is symmetrically applied to all the links, the router periodically
rebalances the traffic on the LAG. You can control the loadbalancing parameters.
Munged QoS Profiles and Load Balancing
To determine whether to use hashed load balancing or subscriber load balancing,
the system munges a QoS profile for a subscriber.
In typical Ethernet configurations, the munged QoS profile for a given subscriber
interface comprises the accumulated rules of the QoS profiles attached below the
subscriber interface in the interface column. Rules in higher-attached QoS profiles
override or eclipse rules in lower-attached QoS profiles. For example, rules from
specific interface attachments such as a VLAN override those from attachments at
S-VLANs or ports.
When applying QoS to LAGs, the system uses a modified algorithm to munge QoS
profile attachments. The system automatically builds the munged QoS profile using
the rules in the QoS profile attached at the LAG interface.
For example, the munged Qos profile for VLAN 0,0 consists of the munge of:
■
Attachment 1—QoS profile attached to the VLAN
■
Attachment 2—QoS profile attached to the S-VLAN
■
Attachment 3—QoS profile attached to the LAG
If there is no QoS profile attached to the LAG, the system locates the lag-default QoS
profile indicated in the
qos-port-type-profile command.
If the resulting QoS profile specifies only Ethernet queues, the system uses the hash
algorithm to balance the links. If the resulting QoS profile specifies any VLAN, IP, or
L2TP-Session queues, then the system uses subscriber load balancing.
802.3ad Link Aggregation and QoS Parameters
You can create parameter instances for IEEE 803.ad LAG interfaces. A parameter
instance for LAG can control an Ethernet port or a node, but you cannot create
parameter instances for the Ethernet interfaces within the LAG.
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QoS for 802.3ad Link Aggregation Interfaces Overview
JUNOSe 11.1.x Quality of Service Configuration Guide