166
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.
, 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
, 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.
Figure 51 Scenario where the Level 2 carrier is an MPLS L3VPN service provider
Provider carrier
MP-IBGP
PE 1
PE 2
CE 2
CE 1
PE 3
PE 4
Customer carrier
Customer carrier
IBGP
IGP
IGP
IGP/LDP/Labeled BGP
Provider carrier
MP-IBGP
PE 1
PE 2
CE 2
CE 1
PE 3
PE 4
Customer carrier
Customer carrier
MP-IBGP
IGP/LDP
IGP/LDP
IGP/LDP/Labeled BGP