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Figure 82 Multi-hop EBGP interconnectivity
In the multi-hop EBGP interconnectivity approach, only one MD needs to be established for all the
ASs, and public network multicast traffic between different ASs is transmitted within this MD.
MD VPN inter-AS option B
In MD VPN inter-AS option B, RPF vector and BGP connector are introduced:
•
RPF vector—Attribute encapsulated in a PIM join message. It is the next hop of BGP MDT route
from the local PE device to the remote PE device. Typically, it is the ASBR in the local AS.
When a device receives the join message with the RPF vector, it first checks whether the RPF
vector is its own IP address. If so, the device removes the RPF vector, and sends the message
to its upstream neighbor according to the route to the remote PE device. Otherwise, it keeps the
RPF vector, looks up the route to the RPF vector, and sends the message to the next hop of the
route. In this way, the PIM message can be forwarded across the ASs and an MDT is
established.
•
BGP connector—Attribute shared by BGP peers when they exchange VPNv4 routes. It is the IP
address of the remote PE device.
The local PE device fills the upstream neighbor address field with the BGP connector in a join
message. This ensures that the message can pass the RPF check on the remote PE device
after it travels along the MT.
For more information about VPN inter-AS option B, see
MPLS Configuration Guide
.
As shown in
:
•
A VPN network involves AS 1 and AS 2.
•
PE 3 and PE 4 are the ASBRs for AS 1 and AS 2, respectively.
•
PE 3 and PE 4 are interconnected through MP-EBGP and treat each other as a P device.
•
PE 3 and PE 4 advertise VPN-IPv4 routes to each other through MP-EBGP.
•
An MT is established between PE 1 and PE 2 for delivering VPN multicast traffic across the
ASs.
