The LINK method establishes one or more Link relationships between the existing resource identified by the Request-URI and other existing resources. The difference between LINK and other methods allowing links to be established between resources is that the LINK method does not allow any message-body to be sent in the request and does not directly result in the creation of new resources.
If the request passes through a cache and the Request-URI identifies a currently cached entity, that entity MUST be removed from the cache. Responses to this method are not cachable.
Caches that implement LINK should invalidate cached responses as defined in section 13.10 for PUT.