IPv6-Link local address

["kernel learner" <kernellearner at gmail.com>]

Hi all,

In IPv6 whenever a NS packet is received,
and if the target address is link local, then second 16 bits from lsb side are fileed with interface index. and while sending NA as reply those bits in target address are made zero. Why is it done?

Acc. to rfc, those 16bits are part of 64 bit interface identifier. why some bits are removed like this? and they are not considered in checksum calculation also. why?

Thanks n Regards

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