H3C Technologies H3C S6800 Series Switches - Manual (Page 185)

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Carrier's carrier
If a customer of the MPLS L3VPN service provider is also a service provider:
• The MPLS L3VPN service provider is called the provider carrier or the Level 1 carrier.
• The customer is called the customer carrier or the Level 2 carrier.
This networking model is referred to as carrier's carrier.
The PEs of the Level 2 carrier directly exchange customer networks over a BGP session. The Level 1 carrier
only learns the backbone networks of the Level 2 carrier, without learning customer networks.
For packets between customer networks to travel through the Level 1 carrier, the PE of the Level 1 carrier
and the CE of the Level 2 carrier must assign labels to the backbone networks of the Level 2 carrier. The
CE of the Level 2 carrier is a PE within the Level 2 carrier network.
Follow these guidelines to assign labels:
• If the PE and the CE are in a same AS, you must configure IGP and LDP between them. If they are
in different ASs, you must configure MP-EBGP to assign labels to IPv4 unicast routes exchanged
between them.
• You must enable MPLS on the CE of the Level 2 carrier regardless of whether the PE and CE are in
the same AS.
A Level 2 carrier can be an ordinary ISP or an MPLS L3VPN service provider.
As shown in
Figure 50 , when the customer carrier is an ordinary ISP, its PEs and CEs run IGP to
communicate with each other. The PEs do not need to run MPLS. PE 3 and PE 4 exchange customer
network routes (IPv4 unicast routes) through an IBGP session.
Figure 50 Scenario where the Level 2 carrier is an ISP
As shown in Figure 51 , when the customer carrier is an MPLS L3VPN service provider, its PEs and CEs
must run IGP and LDP to communicate with each other. PE 3 and PE 4 exchange customer network routes
(VPN-IPv4 routes) through an MP-IBGP session.
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