Suppose there is a PE router,take part in igp mpls,bgp ipv4 with label,vpnv4 and TE.Then when a packet pass the LSR from CE,the LSR will put several label on the packet.Then comes the question:How can the router determine the order of these labels when puting them on the packet.
I think there's two possibal answers:
first,it is define by some document,that's an arbitrary answer;
second,it is relate to the packet process flow.
I wonder what is the truth.I need some detailed explain or document.thanks!