1. Authentication failure: the first user whose authentication path
is along a newly failed server will experience a long delay and
possibly timeout
2. Wrongly deduced states: since the proxy chain is longer than one
hop, a failure further along in the authentication path is
indistinguishable from a failure in the next hop.
3. Inability to determine recovery of a server: only a "live"
authentication request sent to a server that is believed to be
inoperable can lead to the discovery that the server is in
working order again. This issue has been resolved with RFC 5997
[RFC5997].