Per Link Hashing - Alcatel-Lucent 7750 Configuration Manual

Per Link Hashing

The hashing feature described in this section applies to traffic going over LAG and MC-LAG. Per
link hashing ensures all data traffic on a given SAP or network interface uses a single LAG port on
egress. Because all traffic for a given SAP/network interface egresses over a single port, QoS SLA
enforcement for that SAP, network interface is no longer impacted by the property of LAG
(distributing traffic over multiple links). Internally-generated, unique IDs are used to distribute
SAPs/network interface over all active LAG ports. As ports go UP and DOWN, each SAP and
network interface is automatically rehashed so all active LAG ports are always used.
The feature is best suited for deployments when SAPs/network interfaces on a given LAG have
statistically similar BW requirements (since per SAP/network interface hash is used). If more
control is required over which LAG ports SAPs/network interfaces egress on, a LAG link map
profile feature described later in this guide may be used.
Per link hashing, can be enabled on a LAG as long as the following conditions are met:
•
•
•
•
Weighted per-link-hash
Weighted per-link-hash allows higher control in distribution of SAPs/interfaces/subscribers across
LAG links when significant differences in SAPs/interfaces/subscribers bandwidth requirements
could lead to an unbalanced distribution bandwidth utilization over LAG egress. The feature
allows operators to configure for each SAPs/interfaces/subscribers on a LAG one of three 3
unique classes and a weight value to be used to when hashing this service/subscriber across the
LAG links. SAPs/interfaces/subscribers are hashed to LAG links, such that within each class the
total weight of all SAPs/interfaces/subscribers on each LAG link is as close as possible to each
other.
Multiple classes allow grouping of SAPs/interfaces/subscribers by similar bandwidth class/type.
For example a class can represent: voice – negligible bandwidth, Broadband – 10-100Mbps,
Extreme Broadband – 300Mbps and above types of service. If a class and weight are not specified
for a given service or subscriber, values of 1 and 1 are used respectively.
The following algorithm is used to hash SAPs/interfaces/subscribers to LAG egress links:
•
7750 SR Interface Configuration Guide
LAG port-type must be standard.
LAG access adapt-qos must be link or port-fair (for LAGs in mode access or hybrid).
System must be at minimum in chassis mode d (configure system chassis-mode)
LAG mode is access/hybrid and the access adapt-qos mode is distribute include-egr-
hash-cfg
TPSDA subscribers are hashed to a LAG link when subscribers are active, MSE SAPs/
interfaces are hashed to a LAG link when configured
Interface Configuration
Page 127