HP 10500 Series Configuration Manual page 101

Figure 33 Network diagram for inter-AS option B
Inter-AS option B has better scalability than option A.
When adopting the MP-EBGP method, note the following:
• ASBRs do not perform route target filtering on VPN-IPv4 routes that they receive from each other.
Therefore, the ISPs in different ASs must agree on the route exchange.
VPN-IPv4 routes are exchanged only between VPN peers. A VPN site 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 meet 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, which hinders network extension.
Inter-AS option C can solve the problem by making 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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