HP VSR1000 Configuration Manual page 155

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.
To implement MD VPN inter-AS option B, only one MD needs to be established for the two ASs. VPN
multicast data is transmitted between different ASs on the public network within this MD.
As shown in Figure 59:
•
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.
Figure 59 MD VPN inter-AS option B
The establishment of the MDT on the public network is as follows:
PE 1 originates a PIM join message to join the SPT rooted at PE 2. In the join message, the
1.
upstream neighbor address is the IP address of PE 2 (the BGP connector). The RPF vector
attribute is the IP address of PE 3. PE 1 encapsulates the join message as a public network
packet and forwards it through the MTI.
P 1 determines that the RPF vector is not an IP address of its own. It looks up the routing table
2.
for a route to PE 3, and forwards the packet to PE 3.
PE 3 removes the RPF vector because the RPF vector is its own IP address. It fails to find a
3.
BGP MDT route to PE 2, so it encapsulates a new RPF vector (IP address of PE 4) in the packet
and forwards it to PE 4.
PE 4 removes the RPF vector because the RPF vector is its own IP address. It has a local route
4.
to PE 2, so it forwards the packet to P 2, which is the next hop of the route to PE 2.
P 2 sends the packet to PE 2.
5.
PE 2 receives the packet on the MTI and decapsulates the packet. The receiving interface is the
6.
RPF interface of the RPF route back to PE 1 for the join message, and the join message passes
the RPF check. The SPT from PE 1 to PE 2 is established.
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