Addresses of this type were developed due to concerns that the same Interface identifier could be used anytime in multiple communication contexts. In this case it becomes possible for that identifier to be used to correlate seemingly unrelated activity. But privacy extended addresses are considered harmful [DS04] for several reasons:

• They complicate debugging, troubleshooting
• They require frequent updates on the reverse DNS entries
• They allow easier in-prefix address spoofing
• In the current form temporary and forged addresses cannot be distinguished
• They do not improve the prefix privacy

Therefore we do not recommend using privacy extended address as defined in RFC 3041. The updated standard addresses [NDK05] solve some of the problems above. There is also a new IPv6 feature called Cryptographically Generated Addresses (CGA) [RFC3972], which generates a random interface identifier based on the public key of the node. The goal of CGA is to prove ownership of an address and to prevent spoofing and stealing of existing IPv6 addresses.

To prevent using RFC 3041 type of addresses you can use the filtering technique described in the previous section.