shown on 33 page of RFC4364, for inter-AS Mpls VPN, if the /32 host routes are unknown by the ASes, it need 3 labels, who can give an example to explain how the 3 labels works.
thanks in advance
If the /32 routes for the PE routers are made known to the P
routers of each AS, everything works normally. If the /32
routes for the PE routers are NOT made known to the P routers
(other than the ASBRs), then this procedure requires a packet's
ingress PE to put a three-label stack on it. The bottom label
is assigned by the egress PE, corresponding to the packet's
destination address in a particular VRF. The middle label is
assigned by the ASBR, corresponding to the /32 route to the
egress PE. The top label is assigned by the ingress PE's IGP
Next Hop, corresponding to the /32 route to the ASBR.