Operation Manual – MPLS L3VPN
H3C S9500 Series Routing Switches
Chapter 1 MPLS L3VPN Configuration
1-14
VPN 1
CE 1
PE 1
PE 3
VPN 1
CE 3
CE 1
VPN 2
VPN 2
PE 2
PE 4
ASBR 1
(PE)
ASBR 2
(PE)
VPN LSP 1
VPN LSP 2
LSP 1
LSP 2
CE 4
VPN LSP2
MP-EBGP
AS 100
AS 200
M
P
-IBG
P
MP
-IB
G
P
M
P
-IBG
P
M
P-
IB
GP
MPLS backbone
MPLS backbone
Figure 1-10
Network diagram for inter-provider VPN option B
In terms of scalability, inter-provider VPN option B is better than option A.
When adopting MP-EBGP method, note that:
z
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.
z
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.
III. 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. When
every AS needs to exchange a great amount of VPN routes, the ASBRs may become
bottlenecks hindering network extension.
One way to solve the above problem is to make PEs directly exchange VPN-IPv4
routes without the participation of ASBRs:
z
Two ASBRs advertise labeled IPv4 routes to PEs in their respective ASs through
MP-IBGP.
z
The ASBRs neither maintain VPN-IPv4 routes nor advertise VPN-IPv4 routes to
each other.
z
An ASBR maintains labeled IPv4 routes of the PEs in the AS and advertises them
to the peers in the other ASs. The ASBR of an AS also advertises labeled IPv4
routes. Thus, an LSP is established between the ingress PE and egress PE.
z
Between PEs of different ASs, Multi-hop EBGP connections are established to
exchange VPN-IPv4 routes.
