sed for verification of the sender's CGA while the RSA Signature option is then used to protect the messages related to Router and Neighbor discovery. Timestamp and Nonce options are used to prevent replay attacks. The CPS and CPA messages are used to pass information required for discovery of the certification path without loading Router Solicitation and Router Advertisement messages with that information. A node sends CPS to request certification path a router has with one or more nodes' trust anchors included in a Trust Anchor option. The router replies with CPA and includes Trust Anchor options in addition to Certificate option containing a certificate node can use to establish a certification path to a trust anchor. 3.4.10 Neighbor Discovery Proxies In certain deployments, IPv6 nodes that are on the same logical link may not be directly connected into the same physical medium. For example, multiple IPv6 nodes may be con- nected via point-to-point links to a central node, which hears everybody connected through point-to-point links, but none of the nodes on the point-to-point links can hear each other. Another example is a setup where a central node is between different link types, such as between a shared link and a point-to-point link. In such a case nodes in the shared link can hear each other, but not directly the node in the point-to-point link. If allowed by link-layer types, simple bridging would be enough to enable direct node-to-node communications. Unfortunately simple bridging does not work if the link types are different. In order to facilitate communications between nodes that do not hear each other directly, the central node can implement an experimental functionality called 'Neighbor Discovery Proxy' illustrated in Figure 3.14 [76]. The Neighbor Discovery Proxy functionality works SO that the Neighbor Discovery Proxy node listens for all multicast traffic on proxied inter- faces (such as the shared and point-to-point links of Figure 3.14), and selectively forwards or proxies multicast packets t