3com 8807 사용자 가이드
514
C
HAPTER
47: MPLS A
RCHITECTURE
MPLS and Other
Protocols (Routing
Protocols)
When LDP establishes LSP in hop-by-hop mode, the next hop is determined by
using the information, which is usually collected by such routing protocols as IGP,
BGP in each LSR route forwarding table, on the way. However, LDP just uses the
routing information indirectly, rather than associates with various routing
protocols directly.
using the information, which is usually collected by such routing protocols as IGP,
BGP in each LSR route forwarding table, on the way. However, LDP just uses the
routing information indirectly, rather than associates 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. The 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, the application of MPLS VPN requires extending the BGP protocol,
thus the BGP protocol can propagate VPN routing information.
distribution, it is not the sole protocol for label distribution. The 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, the application of MPLS VPN requires extending the BGP protocol,
thus the BGP protocol can propagate VPN routing information.
MPLS Application
(MPLS-based VPN)
To transmit data stream of private network on public network, traditional VPN
uses tunnel protocols like GRE, L2TP, and PPTP. LSP itself is a tunnel on public
network, so there are obvious advantages to implement VPN by MPLS. MPLS VPN
connects the geographically different branches of private network by using LSP,
forming a united network. MPLS VPN also supports the interconnection between
different VPNs.
uses tunnel protocols like GRE, L2TP, and PPTP. LSP itself is a tunnel on public
network, so there are obvious advantages to implement VPN by MPLS. MPLS VPN
connects the geographically different branches of private network by using LSP,
forming a united network. MPLS VPN also supports the interconnection between
different VPNs.
Figure 125 MPLS-Based VPN
The basic structure of MPLS-based VPN is shown in Figure 125. CE is the customer
edge device, and it may either be a router or a switch, or perhaps a host. PE is a
service provider edge router, which is located on the backbone network. PE is
responsible for the management of VPN customers, establishing LSP connection
between various PEs, route allocation among different branches of the same VPN
customer.
edge device, and it may either be a router or a switch, or perhaps a host. PE is a
service provider edge router, which is located on the backbone network. PE is
responsible for the management of VPN customers, establishing LSP connection
between various PEs, route allocation among different branches of the same VPN
customer.
Usually the route allocation between PEs is implemented by using extended BGP.
MPLS VPN supports the IP address multiplexing between different branches and
the interconnection between different VPNs. Compared with traditional route, it is
necessary to add branch and VPN identifier information in VPN route. So, it is
necessary to extend BGP so as to carry VPN routing information.
MPLS VPN supports the IP address multiplexing between different branches and
the interconnection between different VPNs. Compared with traditional route, it is
necessary to add branch and VPN identifier information in VPN route. So, it is
necessary to extend BGP so as to carry VPN routing information.
Private
network branch 2
Private
network branch 1
Backbone network
Private
network branch 3
CE1
PE1
PE3
CE3
PE2
CE2
Private
network branch 2
Private
network branch 1
Backbone network
Private
network branch 3
CE1
PE1
PE3
CE3
PE2
CE2