HP A6600 Configuration Manual page 56

The router automatically chooses an optimal MBGP route by searching its MBGP routing table and
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using the IP address of the packet source as the destination address. The outgoing interface in the
corresponding routing entry is the RPF interface, and the next hop is the RPF neighbor.
The router automatically chooses an optimal multicast static route by searching its multicast static
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routing table and using the IP address of the packet source as the destination address. The
corresponding routing entry explicitly defines the RPF interface and the RPF neighbor.
The router selects one of these three optimal routes as the RPF route. the selection process is as
2.
follows:
If configured to use the longest match principle, the router selects the longest match route from the
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three. If these three routes have the same mask, the router selects the route with the highest priority. If
the three routes have the same priority, the router selects the RPF route according to the sequence of
multicast static route, MBGP route, and unicast route.
If not configured to use the longest match principle, the router selects the route with the highest
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priority. If the three routes have the same priority, the router selects the RPF route according to the
sequence of multicast static route, MBGP route, and unicast route.
The packet source means different things in different situations:
For a packet traveling along the SPT from the multicast source to the receivers or the RP, the packet
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source for RPF check is the multicast source.
For a packet traveling along the RPT from the RP to the receivers, or along the source-side RPT from
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the multicast source to the RP, the packet source for RPF check is the RP.
• For a bootstrap message from the BSR, the packet source for RPF check is the BSR.
For more information about the concepts of SPT, RPT, source-side RPT, RP, and BSR, see
PIM." For more information about multicast across VPNs, see
Implementation of RPF check in multicast
Implementing an RPF check on each received multicast data packet would bring a big burden to the
router. The use of a multicast forwarding table is the solution to this issue. When creating a multicast
routing entry and a multicast forwarding entry for a multicast packet, the router sets the RPF interface of
the packet as the incoming interface of the (S, G) entry. After receiving an (S, G) multicast packet, the
router first searches its multicast forwarding table:
If the corresponding (S, G) entry does not exist in the multicast forwarding table, the packet
1.
undergoes an RPF check. The router creates a multicast routing entry based on the relevant routing
information and adds the entry into the multicast forwarding table, with the RPF interface as the
incoming interface.
If the interface on which the packet actually arrived is the RPF interface, the RPF check succeeds and
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the router forwards the packet to all the outgoing interfaces.
If the interface on which the packet actually arrived is not the RPF interface, the RPF check fails and
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the router discards the packet.
If the corresponding (S, G) entry exists, and the interface on which the packet arrived is the
2.
incoming interface, the router forwards the packet to all the outgoing interfaces.
If the corresponding (S, G) entry exists, but the interface on which the packet arrived is not the
3.
incoming interface in the multicast forwarding table, the multicast packet undergoes an RPF check.
If the RPF interface is the incoming interface of the (S, G) entry, this means the (S, G) entry is correct
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but the packet arrived from a wrong path. The packet will be discarded.
If the RPF interface is not the incoming interface, this means the (S, G) entry has expired, and router
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replaces the incoming interface with the RPF interface. If the interface on which the packet arrived is
"Configuring multicast
45
"Configuring
VPN."