Methods and systems for selectively blocking, allowing and/or reformatting IPv6 headers by traversing devices are provided. According to one embodiment, reputation information regarding observed senders of Internet Protocol (IP) version 6 (IPv6) packets and packet fragments is maintained by a traversing device based on conformity or nonconformity of extension headers contained within the IPv6 packets with respect to a set of security checks performed by the traversing device. When an IPv6 packet or packet fragment is received from a particular source IP address indicated by the reputation information to be associated with one or more nonconformity issues, then dropping, rate limiting or quarantining, by the traversing device, the IPv6 packet or the packet fragment.