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Service Control MPLS/VPN Requirements
VPN Identifier (RD or RT)
Either the Route Distinguisher (RD) attribute or the Route Target (RT) attribute can be used to identify
the VPN. It is required to decide which attribute best reflects the VPN partitioning, and configure the
system accordingly. Note that the configuration is global for all the VPNs, that is, all VPNs must be
identified by the same attribute.
The Route Distinguisher (RD) is generally used to distinguish the distinct VPN routes of separate
customers who connect to the provider, so in most cases the RD is a good partition for the VPNs in the
network. Since the RD is an identifier of the local VRF, and not the target VRF, it can be used to
distinguish between VPNs that transfer information to a common central entity (for example a central
bank, IRS, Port Authority, etc.).
The Route Target (RT) is used to define the destination VPN site. Though it is not intuitive to define the
VPN based on its destination route, it might be easier in some cases. For example, if all the VPN sites
that communicate to a central bank should be treated as a single subscriber, consider using the RT as the
VPN identifier.
It is important to note that this configuration is global. Therefore, if at some point in time, any VPN
would have to be defined by RD, then all the other VPNs must be defined by RD as well. This is a point
to consider when designing the initial deployment.
Service Control MPLS/VPN Requirements
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Topology
Following are the general topology requirements for MPLS/VPN support:
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In a cascade installation:
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Cisco SCE 2000 and SCE 1000 Software Configuration Guide
13-8
Topology, page 13-8
Capacity, page 13-9
Limitations, page 13-10
Backwards Compatibility, page 13-11
The SCE platform is placed in the network between the P routers (Provider MPLS core) and the PE
(Provider Edge) routers.
The subscriber side of the SCE platform is connected toward the PE router.
The network side of the SCE platform is connected toward the P router.
The BGP LEG is installed on the SM, and is placed somewhere in the network.
It speaks with the SCE platform through the management IP.
The two SCE platforms are connected to each other via the cascade interfaces.
The data link between the P and the PE is connected via the other interfaces on each SCE platform,
as described above:
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Subscriber side of each SCE platform connected toward the PE router
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Network side of each SCE platform connected toward the P router
Chapter 13
MPLS/VPN Support
OL-7827-12
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