Interface Configuration
7210 SAS M, T, X, R6, R12, Mxp, S, Sx Interface Configuration Guide Page 51
LACP enhancements allow active lag-member selection based on particular constrains. The
mechanism is based on the IEEE 802.3ax standard so interoperability is ensured.
Active-Standby LAG Operation without LACP
Active/standby LAG is used to provide redundancy while keeping consistency of QOS
enforcement. Some devices do not support LACP and hence an alternative solution is required.
The active/standby decision for LAG member links is local decision driven by pre-configured
selection-criteria. This decision was communicated to remote system using LACP signalling.
As an alternative, the operator can disable the signal transmitted by using power-off option for
standby-signalling in the CLI command at the LAG level at the port member level. As a
consequence, the transmit laser will be switched off for all LAG members in standby mode. On
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.
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