3com 3031 Instruccion De Instalación
MPLS and Other Protocols
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Figure 163 LSP Tunnel
As shown in Figure 163, LSP <R2 R21 R22 R3> is a tunnel between R2 and R3.
Multi-layer label stack
When the packet is sent via LSP tunnel, there will be multiple layers for the label of
the packet. Then, on the ingress and egress of each tunnel, it is necessary to
implement incoming and outgoing operation for the label stack. For each
incoming operation, the label will be added with one layer. And there is no depth
limitation for the label stack from MPLS.
the packet. Then, on the ingress and egress of each tunnel, it is necessary to
implement incoming and outgoing operation for the label stack. For each
incoming operation, the label will be added with one layer. And there is no depth
limitation for the label stack from MPLS.
The labels are organized according to the principle “last in first out” in the label
stack. MPLS processes labels beginning from the top of the stack.
stack. MPLS processes labels beginning from the top of the stack.
Suppose that a packet has a label stack depth of m, then the label at the bottom
of the stack is the first level label, and the label at the top of the stack is the label
level of m. A packet with no label can be regarded as a blank label stack (namely,
the label stack depth is zero).
of the stack is the first level label, and the label at the top of the stack is the label
level of m. A packet with no label can be regarded as a blank label stack (namely,
the label stack depth is zero).
MPLS and Other
Protocols
Protocols
This section describes how MPLS operates with other protocols.
MPLS and Routing
Protocols
When LDP establishes LSP in hop-by-hop mode, the next hop will be determined
by using the information that is usually collected via routing protocols such as IGP,
BGP in each LSR route forwarding table on the way. However, LDP just uses the
routing information indirectly, rather than being associated with various routing
protocols directly.
by using the information that is usually collected via routing protocols such as IGP,
BGP in each LSR route forwarding table on the way. However, LDP just uses the
routing information indirectly, rather than being associated with various routing
protocols directly.
On the other hand, although LDP is the special protocol for implementing label
distribution, it is not the sole protocol for label distribution. Existing protocols such
as BGP, RSVP, after being extended, can also support MPLS label distribution. For
some MPLS applications, it is also necessary to extend some routing protocols. For
example, MPLS-based VPN application needs the extension of BGP so that the BGP
is capable of supporting the sending of VPN routing information.
distribution, it is not the sole protocol for label distribution. Existing protocols such
as BGP, RSVP, after being extended, can also support MPLS label distribution. For
some MPLS applications, it is also necessary to extend some routing protocols. For
example, MPLS-based VPN application needs the extension of BGP so that the BGP
is capable of supporting the sending of VPN routing information.
MPLS Application
This section describes the use of MPLS with VPN and QoS.
MPLS-Based VPN
For traditional VPN, the transmission of the data flow between private networks
on the public network typically uses such tunneling protocols as GRE, L2TP and
PPTP, and LSP itself is the tunnel on the public network. The implementation of
VPN using MPLS is a natural advantage. MPLS-based VPN connects the
geographically different branches of private network by using LSP, forming a
united network. MPLS-based VPN also supports the interconnection between
different VPNs.
on the public network typically uses such tunneling protocols as GRE, L2TP and
PPTP, and LSP itself is the tunnel on the public network. The implementation of
VPN using MPLS is a natural advantage. MPLS-based VPN connects the
geographically different branches of private network by using LSP, forming a
united network. MPLS-based VPN also supports the interconnection between
different VPNs.
R1
R2
R3
R4
R21
R22
Layer 1
Layer 2