An additional function performed by VNET+ is to set the peer credential on sockets based on the xid of the peer. For example, if slice X connections to a port hosted by slice Y on a given node, then the peer credential of the socket from X's point of view will be the xid of Y and vice versa. Note that the xid is the uid of a slice on a PlanetLab node. This method can be used to authenticate a service running on a node.
To evaluate the peer credentials of a socket, you need to call getsockopt with the SO_PEERCRED socket option.