Alcatel-Lucent 7750 Configuration Manual page 128

LAG and ECMP Hashing
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Optionally an operator can use, a "tools perform lag load-balance" command to manually re-
balance ALL weighted per-link-hashed SAPs/interfaces/subscribers on a LAG. The rebalance
follows the algorithm as used on a link failure moving SAPs/interfaces/subscribers to different
LAG links to minimize SAPs/interfaces/subscribers impacted.
An optional time-delay for off-peak rebalance can be specified. If LAG is moved from weighted
per-link-hash while the load-balance is being time delayed, the time delay will be canceled and no
rebalancing will happen. If LAG or its links change operational, administrative status, the time
delay will not be impacted and will execute once the delay timer expires.
The following caveats exist:
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For a new SAP/interface/subscriber to be hashed to an egress LAG link:
Select active link with the smallest current weight for the SAP/network/subscriber class
(lowest link id tie-breaker)
On a LAG link failure:
→ Only SAPs/interfaces/subscribers s on a failed link are rehashed over the remaining
active links
→ Processing order: Per class from lowest numerical, within each class per weight from
highest numerical value
LAG link recovery/new link added to a LAG
auto-rebalance disabled: Existing SAPs/interfaces/subscribers remain on the currently
active links, new SAPs/interfaces/subscribers naturally prefer the new link until balance
reached.
auto-rebalance is enabled: When a new port is added to a LAG a non-configurable 5
second rebalance timer is started. Upon timer expiry, all existing SAPs/interfaces/
subscribers are rebalanced across all active LAG links minimizing the number of SAPs/
interfaces/subscribers moved to achieve rebalance. The rebalance timer is restarted if a
new link is added while the timer is running. If a port bounces 5 times within a 5 second
interval, the port is quarantined for10 seconds. This behavior is not configurable.
On a LAG start-up, the rebalance timer is always started irrespective of auto-rebalance
configuration to avoid hashing SAPs/interfaces/subscribers to a LAG before ports have a
chance to come UP.
When weighted per-link-hash is deployed on a given LAG, no other methods of hash for
subscribers/SAPs/interfaces on that LAG (like service hash or LAG link map profile)
should be deployed, since the weighted hash is not able to account for load placed on LAG
links by subscriber/SAPs/interfaces using the other hash methods.
Weighted per-link-hash is not supported with mixed-speed LAGs and for network
interfaces.
For TPSDA model:
→ only 1:1 (subscriber to SAP) model is supported and weight/class should not be
enabled on a SAP.
7750 SR Interface Configuration Guide