3Com MSR 50 Series Configuration Manual page 1471

to excessive VPN-IPv4 routes on the PEs. Moreover, the requirement to create a
separate subinterface for each VPN also calls for higher performance of the PEs.
Inter-provider VPN option B
In this kind of solution, two ASBRs use MP-EBGP to exchange labeled VPN-IPv4
routes that they have obtained from the PEs in their respective ASs.
As shown in Figure 414, the routes are advertised through the following steps:
1 PEs in AS 100 advertise labeled VPN-IPv4 routes to the ASBR PE of AS 100 or the
route reflector (RR) for the ASBR PE through MP-IBGP.
2 The ASBR PE advertises labeled VPN-IPv4 routes to the ASBR PE of AS 200 through
MP-EBGP.
3 The ASBR PE of AS 200 advertises labeled VPN-IPv4 routes to PEs in AS 200 or to
the RR for the PEs through MP-IBGP.
The ASBRs must perform the special processing on the labeled VPN-IPv4 routes,
which is also called ASBR extension method.
Figure 414 Network diagram for inter-provider VPN option B
VPN 1
CE 1
PE 1
MPLS backbone
AS 100
PE 2
VPN LSP 1
CE 1
LSP 1
VPN 2
In terms of scalability, inter-provider VPN option B is better than option A.
When adopting MP-EBGP method, note that:
ASBRs perform no VPN target filtering on VPN-IPv4 routes that they receive
■
from each other. Therefore, the ISPs in different ASs that exchange VPN-IPv4
routes need to agree on the route exchange.
VPN-IPv4 routes are exchanged only between VPN peers. A VPN user can
■
exchange VPN-IPv4 routes neither with the public network nor with MP-EBGP
peers with whom it has not reached agreement on the route exchange.
Inter-provider VPN option C
The above two kinds of solutions can satisfy the needs for inter-provider VPNs.
However, they require that the ASBRs maintain and advertise VPN-IPv4 routes.
ASBR 2
ASBR 1
MP-EBGP
(PE)
(PE)
VPN LSP 2
VPN LSP2
LSP 2
MPLS L3VPN Overview
VPN 1
CE 3
PE 3
MPLS backbone
AS 200
PE 4
CE 4
VPN 2
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