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JunosE 11.3.x Quality of Service Configuration Guide
Munged QoS Profiles and Load Balancing
802.3ad Link Aggregation and QoS Parameters
176
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.
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.
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.
For example, a LAG instance can specify a shaping rate of 100 Mbps on an Ethernet port
or a group node. The system shapes all Ethernet ports or group nodes to the same rate
within the LAG. Using load balancing, the system strives to balance the traffic each link
equally.
Copyright © 2010, Juniper Networks, Inc.
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