Explicit Per Link Hash Using Lag Link Mapping Profiles - Alcatel-Lucent 7750 Configuration Manual

LAG and ECMP Hashing

Explicit Per Link Hash Using LAG Link Mapping Profiles

The hashing feature described in this section applies to traffic going over LAG and MC-LAG.
LAG link mapping profile feature gives operators full control of which links SAPs/network
interface use on a LAG egress and how the traffic is rehashed on a LAG link failure. Some
benefits that such functionality provides include:
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To enable LAG Link Mapping Profile Feature on a given LAG, operators configure one or more of
the available LAG link mapping profiles on the LAG and then assign that profile(s) to all or a
subset of SAPs and network interfaces as needed. Enabling per LAG link Mapping Profile is
allowed on a LAG with services configured, a small outage may take place as result of re-hashing
SAP/network interface when a lag profile is assigned to it.
Each LAG link mapping profile allows operators to configure:
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Ability to perform management level admission control onto LAG ports thus increasing
overall LAG BW utilization and controlling LAG behavior on a port failure.
Ability to strictly enforce QoS contract on egress for a SAP/network interface or a group
of SAPs/network interfaces by forcing it/them to egress over a single port and using
access adapt-qos link or port-fair mode.
Primary link—defines a port of the LAG to be used by a SAP/network interface when the
port is UP. Note that a port cannot be removed from a LAG if it is part of any LAG link
profile.
Secondary link—defines a port of the LAG to be used by a SAP/network interface as a
backup when the primary link is not available (not configured or down) and the secondary
link is UP.
Mode of operation when neither primary, nor secondary links are available (not
configured or down):
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discard – traffic for a given SAP/network interface will be dropped to protect
other SAPs/network interfaces from being impacted by re-hashing these SAPs/
network interfaces over remaining active LAG ports.
Note: SAP/network interface status will not be affected when primary and
secondary links are unavailable, unless an OAM mechanism that follows the data
path hashing on egress is used and will cause a SAP/network interface to go down
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per-link-hash – traffic for a given SAP/network interface will be re-hashed over
remaining active ports of a LAG links using per-link-hashing algorithm. This
behavior ensures SAP/network interfaces using this profile will be given available
resources of other active LAG ports even if that means impacting other SAP/
network interfaces on the LAG. The system will use the QoS configuration to
provide fairness and priority if congestion is caused by the default-hash recovery.
7750 SR Interface Configuration Guide