I have a question about unrecognized BGP path attribute. According to
RFC4271, when a BGP router sees an UPDATE with an unrecognized
optional and transitive path attribute, it should retain the
attribute, and if the path is selected, it should propagate the
attribute to its neighbors. My question is, if later the router sees
an update to the path in which only the unrecognized attribute has
changed, should it immediately propagate the change to its neighbors?
My guess is a yes, but I'm not sure because it's not explicitly
written down in the RFC.
Another question is, in such a case, what will the current routers
from different vendors do? Anyone has any experience on this?