Инструкции По Установке для 3com S7906E

1-11

Figure 1-8 Network diagram for inter-provider VPN option B

VPN 1

CE 1

PE 1

PE 3

VPN 1

CE 3

CE 2

VPN 2

PE 2

PE 4

ASBR 1

(PE)

ASBR 2

(PE)

VPN LSP 1

VPN LSP 3

LSP 1

LSP 2

CE 4

VPN LSP2

MP-EBGP

AS 100

AS 200

-IBG

-IB

-IBG

P-

IBGP

MPLS backbone

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. 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:

Two ASBRs advertise labeled IPv4 routes to PEs in their respective ASs through MP-IBGP.

The ASBRs neither maintain VPN-IPv4 routes nor advertise VPN-IPv4 routes to each other.

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 another AS also advertises labeled IPv4 routes. Thus, an LSP is

established between the ingress PE and egress PE.

Between PEs of different ASs, Multi-hop EBGP connections are established to exchange

VPN-IPv4 routes.