LAG
Page 40 7210 SAS M, T, X, R6, R12, Mxp Interface Configu-
ration Guide
switch over (active-links failed) the laser will be switched on all LAG members will become
active.
Note that this mode of operation cannot detect physical failures on the standby link, which means
that the network operator cannot be certain that the standby links are capable to take over in case
of active-links failure. This is an inherit limitation of this operational mode.
When LACP goes down on a standby link, a warning message announcing that LACP has expired
on the corresponding member port is printed in log 99 on the other end.
The operation where standby ports are powered down is mutually exclusive with LACP and,
therefore, is modelled as separate mode of LACP operation of power-off. For this mode, the
selection-criteria best-port can be used. This criteria means that it will be always a sub-group with
the best-port (the highest priority port) which will be chosen to be used as active sub-group.
It will not be possible to have an active LACP in power-off mode before the correct selection
criteria is selected.
LAG Subgroups
LACP is used to make selection of active links predictable and compatible with any vendor
equipment. Refer to the IEEE STD 802.3-2002, Section 3, Clause 43.6.1 standard which describes
how LACP allows stand-by and active signalling.
The 7210 SAS-M,X,T, R6, R12, and Mxp implementation of LACP supports the following:
• A given LAG member can be assigned to sub-groups. The selection algorithm then
assures that only members of a single sub-group are selected as active links.
• The selection algorithm is effective only if LACP is enabled on a given LAG. At the same
time, it is assumed that connected system has also LACP enabled (active or passive
mode).
• The algorithm will select active links based on following criteria:
→ Depending on selection-criteria setting either the sub-group with the highest number
of eligible links or the sub-group with the highest aggregate weight of all eligible
members is selected first.
→ If multiple groups satisfy the selection criteria, the sub-group being currently active
remains active. Initially, the sub-group containing the highest priority eligible link is
selected.
→ Only links pertaining to a single sub-group are active at any time.
→ An eligible member refers to a LAG member link which can potentially become
active. This means it is operationally up, and if the slave-to-partner flag is set, the
remote system did not disable its use (by signalling stand-by).
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