Architecture Of Mpls - H3C S9500 Series Operation Manual

Operation Manual – MPLS Basics
H3C S9500 Series Routing Switches
If the path that a tunnel traverses is exactly the hop-by-hop route established by the
routing protocol, the tunnel is called a hop-by-hop routed tunnel. Otherwise, the tunnel
is called an explicitly routed tunnel.
VII. Multi-level label stack
MPLS allows a packet to carry a number of labels organized as a last-in first-out (LIFO)
stack, which is called a label stack. A packet with a label stack can travel along more
than one level of LSP tunnel. At the ingress and egress of each tunnel, these
operations can be performed on the top of a stack: PUSH and POP.
MPLS has no limit to the depth of a label stack. For a label stack with a depth of m, the
label at the bottom is of level 1, while the label at the top has a level of m. An unlabeled
packet can be considered as a packet with an empty label stack, that is, a label stack
whose depth is 0.

1.1.2 Architecture of MPLS

I. Structure of the MPLS network
As shown in
routing or administrative domain form an MPLS domain.
In an MPLS domain, LSRs residing at the domain border to connect with other
networks are label edge routers (LERs), while those within the MPLS domain are core
LSRs. All core LSRs, which can be routers running MPLS or ATM-LSRs upgraded from
ATM switches, use MPLS to communicate, while LERs interact with devices outside the
domain that use traditional IP technologies.
Each packet entering an MPLS network is labeled on the ingress LER and then
forwarded along an LSP to the egress LER. All the intermediate LSRs are called transit
LSRs.
Ingress
IP network
Figure 1-4 Structure of the MPLS network
Figure 1-4, the element of an MPLS network is LSR. LSRs in the same
LSP
Transit
Chapter 1 MPLS Basics Configuration
1-5
Egress
IP network