IPv6 Unkown header extension

[Paul Koene]

L.S.,

every once in a while I see the following messages filling the logs on my FreeBSD installations:
IPFW2: IPV6 - Unknown Extension Header(128), ext_hd=0

I am somewhat curious why this message occurs. Did I configure something wrong, Is there an implementation defect in an existing ipv6 stack that these packets try to abuse or is this part of an OS fingerprinting technique or something?

Kind regards,

Paul Koene