HP 6125XLG Ip Multicast Configuration Manual page 264

RPF check implementation in IPv6 multicast
Implementing an RPF check on each received IPv6 multicast packet would heavily burden the router. The
use of an IPv6 multicast forwarding table is the solution to this issue. When the router creates an IPv6
multicast forwarding entry for an IPv6 multicast packet, it sets the RPF interface of the packet as the
incoming interface of the forwarding entry. After the router receives an IPv6 multicast packet, it searches
its IPv6 multicast forwarding table for a matching forwarding entry as follows:
• If no match is found, the router first determines the RPF route back to the packet source. Then, it
creates a forwarding entry with the RPF interface as the incoming interface and makes the following
judgments:
If the receiving interface is the RPF interface, the RPF check succeeds and the router forwards the
packet out of all outgoing interfaces.
If the receiving interface is not the RPF interface, the RPF check fails and the router discards the
packet.
If a match is found and the receiving interface is the incoming interface of the forwarding entry, the
•
router forwards the packet out of all outgoing interfaces.
If a match is found but the receiving interface is not the incoming interface of the forwarding entry,
•
the router determines the RPF route back to the packet source and makes the following judgments:
If the RPF interface is the incoming interface, it means that the forwarding entry is correct, but
the packet traveled along a wrong path. The router discards the packet.
If the RPF interface is not the incoming interface, it means that the forwarding entry has expired,
and the router replaces the incoming interface with the RPF interface. If the receiving interface
is the RPF interface, the router forwards the packet out of all outgoing interfaces. Otherwise, it
discards the packet.
Figure 79 RPF check process
IPv6 Routing Table on Switch C
Destination/Prefix
2000::/16
Source
2000::101/16
As shown in
packets travel along the SPT from the multicast source to the receivers. The IPv6 multicast forwarding table
on Switch C contains the (S, G) entry, with VLAN-interface 20 as the RPF interface.
If an IPv6 multicast packet arrives at Switch C on VLAN-interface 20, Switch C forwards the packet
•
out of all outgoing interfaces.
If an IPv6 multicast packet arrives at Switch C on VLAN-interface 10, Switch C performs an RPF
•
check on the packet. Switch C searches its IPv6 unicast routing table and finds that the outgoing
Interface
Vlan-int20
Switch A
IPv6 Multicast packets
Figure 79, assume that IPv6 unicast routes are available in the network and IPv6 multicast
Switch B
Vlan-int10
Vlan-int10
Vlan-int20
Switch C
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Receiver
Receiver