HP 10500 SERIES Configuration Manual page 246

Figure 20 Network diagram for inter-AS option B
In terms of scalability, inter-AS option B is better than option A.
When adopting the MP-EBGP method, note the following:
ASBRs perform no route target filtering on VPN-IPv4 routes that they receive from each other.
•
Therefore, the ISPs in different ASs that exchange VPN-IPv4 routes must 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-AS option C
The Inter-AS option A and option B solutions can satisfy the needs for inter-AS 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 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.
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