to switch b the first two messages are normal after the split switch a informs b of the change in system id using a message which has a new system id sw 1 but in place of the partner 39 s id sends the superseded system id i e sw 3 in a manner shown in fig9 by square brackets which enables switch b to distinguish the message as one that conveys the superseded system id switch a can determine from the fourth message that switch b has received the change of system id switch a can now stop reporting as shown by the fifth message the change of system id since switch b is a compliant switch it can now update all configuration information that it held for the old system id to refer to the new system id fig1 shows a comparative example similar to fig9 wherein switch b does not have a modified link aggregator that can interpret the field shown as partner sw 3 in fig9 switch b is denoted u2018 incompatible u2019 the exchanges are as before the difference will be that switch b will merely operate according to the existing protocol switches a and b now agree on the systems at each end of the link so they each configure the aggregate link even though switch b does not recognise switch a as the partner it previously knew fig1 and 12 illustrate an aggregating system which splits and the lacp messages that pass between the various linked ports according.