Инструкции По Установке для 3com S7906E
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For information about RSVP, refer to MPLS TE Configuration in the MPLS Volume.
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For information about BGP, refer to BGP Configuration in the IP Routing Volume.
LSP tunneling
MPLS supports LSP tunneling.
An LSR and its downstream LSR on an LSP are not necessarily on a path provided by the routing
protocol. That is, MPLS supports establishing an LSP along a path different from that established by the
routing protocol. Such an LSP is called an LSP tunnel, and the two LSRs are respectively the start point
and end point of the LSP tunnel. For example, the LSP <R2→R21→R22→R3> in
protocol. That is, MPLS supports establishing an LSP along a path different from that established by the
routing protocol. Such an LSP is called an LSP tunnel, and the two LSRs are respectively the start point
and end point of the LSP tunnel. For example, the LSP <R2→R21→R22→R3> in
is a tunnel
between R2 and R3. This tunneling technology does not use the traditional network layer encapsulation
tunneling technology.
tunneling technology.
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.
tunnel is called a hop-by-hop routed tunnel. Otherwise, the tunnel is called an explicitly routed tunnel.
Multi-level label stack
MPLS allows a packet to carry multiple levels of labels organized as a last-in first-out (LIFO) stack,
which is called a label stack. A packet with multiple levels of labels can travel along more than one level
of LSP tunnel. The ingress and egress of each tunnel perform Push and Pop operations respectively on
the top of a stack.
which is called a label stack. A packet with multiple levels of labels can travel along more than one level
of LSP tunnel. The ingress and egress of each tunnel perform Push and Pop operations respectively on
the top of a stack.
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.
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.
Architecture of MPLS
Structure of the MPLS network
As shown in
, the element of an MPLS network is LSR. LSRs in the same routing or
administrative domain form an MPLS domain.
In an MPLS domain, LSRs residing at the domain border and connected 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.
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.
to the egress LER. All the intermediate LSRs are called transit LSRs.