Lag And Ecmp Hashing - Alcatel-Lucent 7750 Configuration Manual

LAG and ECMP Hashing

LAG and ECMP Hashing
When a requirement exists to increase the available bandwidth for a logical link that exceeds the
physical bandwidth or add redundancy for a physical link, typically one of two methods is applied:
equal cost multi-path (ECMP) or Link Aggregation (LAG). A system can deploy both at the same
time using ECMP of two or more Link Aggregation Groups (LAG) and/or single links.
Different types of hashing algorithms can be employed to achieve one of the following objectives:
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These hashing methods are described in the following subsections. Although multiple hashing
options may be configured for a given flow at the same time, only one method will be selected to
hash the traffic based on the following decreasing priority order:
For ECMP load balancing:
1. Consistent per service hashing
2. Per flow hashing
For LAG load balancing:
1. LAG link map profile
2. Per link hash
3. Consistent per service hashing
4. Per flow hashing
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ECMP and LAG load balancing should be influenced solely by the offered flow packet.
This is referred to as per-flow hashing.
ECMP and LAG load balancing should maintain consistent forwarding within a given
service. This is achieved using consistent per-service hashing.
LAG load balancing should maintain consistent forwarding on egress over a single LAG
port for a specific network interface, SAP, etc. This is referred as per link hashing
(including explicit per link hashing with LAG link map profiles). Note that if multiple
ECMP paths use a LAG with per link hashing, the ECMP load balancing is done using
either per flow or consistent per service hashing.
7750 SR Interface Configuration Guide