3Com MSR 50 Series, Руководство по настройке

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1468 C
HAPTER
79: MPLS L3VPN C
ONFIGURATION
Routing information exchange from the local CE to the ingress PE
After establishing an adjacency with the directly connected PE, a CE advertises its
VPN routing information to the PE.
The route between the CE and the PE can be a static route, RIP route, OSPF route,
IS-IS route, or BGP route. No matter which routing protocol is used, the CE always
advertises standard IPv4 routes to the PE.
Routing information exchange from the ingress PE to the egress PE
After learning the VPN routing information from the CE, the ingress PE adds RDs
and VPN targets for these standard IPv4 routes to form VPN-IPv4 routes, and
maintains them for the VPN instance created for the CE.
Then, the ingress PE advertises the VPN-IPv4 routes to the egress PE through
MP-BGP.
Finally, the egress PE compares the export target attribute of the VPN-IPv4 routes
with the import target attribute that it maintains for the VPN instance and
determines whether to add the routes to the routing table of the VPN instance.
PEs use IGP to ensure the connectivity between them.
Routing information exchange from the egress PE to the remote CE
A remote CE can learn VPN routes from the egress PE in a number of ways. The
routes can be static routes, RIP routes, OSPF routes, IS-IS routes, or EBGP routes.
The exchange of routing information between the egress PE and the remote CE is
the same as that between the local CE and the ingress PE.
Carrier’s Carrier Introduction to carrier’s carrier
It is possible that a customer of the MPLS L3VPN service provider is also a service
provider. In this case, the MPLS L3VPN service provider is called the provider carrier
or the Level 1 carrier, while the customer is called the customer carrier or the Level
2 carrier. This networking model is referred to as carrier’s carrier. In this model, the
Level 2 service provider serves as a CE of the Level 1 service provider.
For good scalability, the Level 1 carrier does not inject the external routes of a Level
2 carrier; it only injects routes for switching packets from different sites of the
Level 2 carrier. The external routes maintained by a Level 2 carrier are exchanged
through BGP sessions established between related routes of the Level 2 carrier.
This can greatly reduce the number of routes maintained by the Level 1 carrier
network.
Implementation of carrier’s carrier
Compared to the common MPLS L3VPN, the carrier’s carrier is different mainly
because a CE of a Level 2 carrier accesses a PE of the Level 1 carrier:
■
If the PE of the Level 1 carrier and the CE of the Level 2 carrier are in a same
AS, configure IGP and LDP between them.
■
If the PE of the Level 1 carrier and the CE of the Level 2 carrier are not in the
same AS, configure MP-EBGP between them to label the routes exchanged.