3com S7906E 설치 설명서

 

1-13 

routes of the Level 2 carrier. This can greatly reduce the number of routes maintained by the Level 1 

carrier network. 

Compared with the common MPLS L3VPN, the carrier’s carrier is different because of the way in which 

a CE of a Level 1 carrier, that is, a Level 2 carrier, accesses a PE of the Level 1 carrier: 

z 

If the PE and the CE are in a same AS, you need to configure IGP and LDP between them. 

z 

If the PE and the CE are not in the same AS, you need to configure MP-EBGP to label the routes 

exchanged between them. 

In either case, you need to enable MPLS on the CE of the Level 1 carrier. Moreover, the CE holds the 

VPN routes of the Level 2 carrier, but it does not advertise the routes to the PE of the Level 1 carrier; it 

only exchanges the routes with other PEs of the Level 2 carrier. 

A Level 2 carrier can be an ordinary ISP or an MPLS L3VPN service provider. 

When the Level 2 carrier is an ordinary ISP, its PEs run IGP to communicate with the CEs, rather than 

MPLS. As shown in

 Figure 1-11

, PE 3 and PE 4 exchange VPN routes of the Level 2 carrier through 

IBGP sessions. 

Figure 1-11 Scenario where the Level 2 carrier is an ISP 

Level 1 carrier

MP-IBGP

PE 1

PE 2

CE 2

CE 1

PE 3

PE 4

Level 2 carrier

Level 2 carrier

IBGP

IGP

IGP

IGP/LDP/Labeled BGP

 

 

When the Level 2 carrier is an MPLS L3VPN service provider, its PEs need to run IGP and LDP to 

communicate with CEs. As shown in

 Figure 1-12

, PE 3 and PE 4 exchange VPN routes of the Level 2 

carrier through MP-IBGP sessions.